Implementing parrallel processing in C# code

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C#

I was trying to write one code that needs to fetch the old values stored in some proprietary data base.
To fetch the data, some API and associated functions are provided.The code is as follows.

Now if I run this code, it takes almost 355 seconds. I have measured the time of execution for one point and it took almost 10 seconds(in an avg) to do that.
The test was done with approximately 37 such 'pnt' and it took almost 355 seconds to fetch the required values.The I need to export the same to excel
also.But exporting to excel is not time consuming compared to fetching of data from a time series database through predefined APIs.
I do not have any control in the APIs and I can not do anything on the same.
Considering all this, can I implement parallel processing.I have machine with 24 cores CPU where the program needs to be run.
If somebody can tell me how to implement the same in the code it will be helpful for me.
I was reading some article in this regard, but it seems difficult for me to implement in the code.
If some one cane help me out implementing parallel processing in this code, it will be a great help in reducing time taken by the program.

What I have tried:

int i = 0, j = 0;
                string pnt = "";
                TimeSpan span;
                if (periodtime.SelectedIndex == 0)
                {
                    span = TimeSpan.FromSeconds(Convert.ToInt16(periodval.Text));
                }
                else if (periodtime.SelectedIndex == 1)
                {
                    span = TimeSpan.FromMinutes(Convert.ToInt16(periodval.Text));
                }
                else
                {
                    span = TimeSpan.FromHours(Convert.ToInt16(periodval.Text));
                }	
          	uint s = 0;
                double dval = 0;
                DateTime ts = DateTime.Now;
                string st = "";
                int nRet = 0;
foreach (string slpnt in pntid)
                {

//==========================================================================================
/*The point consist of a collection of strings separated by .,$ etc.It is defined inside a text file.The code reads the whole line and split a particular portion (required one) that we need to pass to API's function.*/
		  //That portion is stored in 'pnt' variable. 
                   pnt = slpnt.Split('-')[0].Split('$')[0];
                    i = 0;
                   span = TimeSpan.FromHours(24);
                   //GetHistMin is a function(Part of an application API) to fetch historical minimum values stored historixcal information database.Hence if .nRet =0 , it enters the loop.
//Here the time range is from Convert.ToDateTime(Fdt.Text + " 00:00:00" =00:00:00 hrs to 24:00:00 hrs (Convert.ToDateTime(Fdt.Text + " 00:00:00").AddHours(24)
/*Span is user given  and here it is 30 seconds.Please note that it is a large data base and for 24 hrs we approximately have to search 4000 samples for a pnt variable and get the minimum out of it.We need to fetch such 50 pnt in minimum to get the desired result.*/
nRet = History.GetHistMin(pnt, Convert.ToDateTime(Fdt.Text + " 00:00:00"), Convert.ToDateTime(Fdt.Text + " 00:00:00").AddHours(24), span, out s);
                   if (nRet == 0)
                   {
                       nRet = History.GetNextHist(s, out dval, out  ts, out st);
					   //GetNextHist is used to collect the resulting value the returned by GetHistMin(). 
                       if (j == 0)
                       {
//Doing the required calculation and adding it to new row of data table.
                           dr = dt.NewRow();
                           dr[0] = "Minimum(of the day)";
                           if (slpnt.Contains("$"))
                           {
                           dr["C" + j.ToString()] = Math.Round(dval, 2);

                           }
                           else
                           {
                           dr["C" + j.ToString()] = Math.Round(dval, 1);
                           }
                           dt.Rows.Add(dr);
                         }
                       else
                 {
                           if (slpnt.Contains("$"))
                 {
                dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 2);
                 }
                           else
                 {
                dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 1);
                 }
             }
         } 

//==========================================================

//Like Minimum, it is calculating the Maximum of the day value.
                  nRet = History.GetHistMax(pnt, Convert.ToDateTime(Fdt.Text + " 00:00:00"), Convert.ToDateTime(Fdt.Text + " 00:00:00").AddHours(24), span, out s);
                   if (nRet == 0)
                   {

                       nRet = History.GetNextHist(s, out dval, out  ts, out st);
                       if (j == 0)
                       {
                           dr = dt.NewRow();
                           dr[0] = "Maximum(of the day)";
                           if (slpnt.Contains("$"))
                           {
                               dr["C" + j.ToString()] = Math.Round(dval, 2);
                           }
                           else
                           {
                               dr["C" + j.ToString()] = Math.Round(dval, 1);
                           }
                           dt.Rows.Add(dr);
                           }
                       else
                       {
                           if (slpnt.Contains("$"))
                           {
         dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 2);
                           }
                           else
                           {
         dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 1);
                           }
                        }			   
                    }  

//=========================================================================================================================

//Like Minimum, it is calculating the Average of the day value.
                    nRet = History.GetHistAvg(pnt, Convert.ToDateTime(Fdt.Text + " 00:00:00"), Convert.ToDateTime(Fdt.Text + " 00:00:00").AddHours(24), span, out s);
                    
                    if (nRet == 0)
                    {
                        nRet = History.GetNextHist(s, out dval, out  ts, out st);
                        if (j == 0)
                        {
                            dr = dt.NewRow();
                            dr[0] = "Average(of the day)";
                            if (slpnt.Contains("$"))
                            {
                                dr["C" + j.ToString()] = Math.Round(dval, 2);
                            }
                            else
                            {
                                dr["C" + j.ToString()] = Math.Round(dval, 1);
                            }
                            dt.Rows.Add(dr);
                        }
                        else
                        {
                            if (slpnt.Contains("$"))
                            {
              dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 2);
                            }
                            else
                            {
              dt.Rows[dt.Rows.Count - 1]["C" + j.ToString()] = Math.Round(dval, 1);
                            }
                        }
                    }
	j++;
}