How do I... Datagridview selected row max value

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DataGridView

Hello,
I'm pulling data into my datagridview table via sql. I want to generate more than the ID number in any row I choose and use it when creating a new record. Normally I can produce more of the last record I chose, but when I make a selection in any row, I want the highest value according to the ID number there. Hope I was able to explain my problem.

What I have tried:

i have tried this code

im using this code below the lines.

public void Code_Create()
        {
            Valuedetails u = new Valuedetails();
            conn.Open();
            SqlCommand comm = new SqlCommand("SELECT max(VALUEID) from VALUES_1 WHERE VALUEID=@VALUEID", conn);
            comm.Parameters.Add("@VALUEID", SqlDbType.VarChar).Value = Variables.valueID;
            u.ValueID = Convert.ToString(comm.ExecuteScalar());
            conn.Close();
            int kod = int.Parse(Regex.Replace(u.ValueID, "[^0-9]", "")) + 1;
            string zeroStr = Regex.Replace(u.ValueID, "[^0-9]", "");
            string newZeroStr = "";
            for (int x = 0; x < zeroStr.Length; x++)
                if (zeroStr[x] == '0') newZeroStr = newZeroStr + "0";
                else { };
            string newVal = Regex.Replace(u.ValueID, "[0-9]", "") + newZeroStr + kod;
            txtvalueID.Text = newVal;            
        }

Program's view;

Code  |   Details
0001  | Pencil
0002  | Paper
0003  | Rubber
tk22  | Battery
tk23  | Glass
................

if i select 002 | Paper, my code has to give new ID code 0004, or select tk22 | Battery has to give me new record code tk24