how to remove the rows in gridview in asp.net

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C#

ASP.NET

protected void dropdownlist1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (dropdownlist1.SelectedItem.ToString() == "Poor")
        {
            SetDropdowndetails("dropdownlist1", 1);
        }
        else
        {
             Selectednotpoor();
        }
    }

    private void SetDropdowndetails(string Dropdownname, Int32 Dropdownid)
    {
            SelectedDropdown = Dropdownname.ToString();
            hfnegativefeedback.Value = Dropdownid.ToString();
            Negativepnlpopup();
    }

    
    private void Negativepnlpopup()
    {
        try
        {
           
            textbox1.Text = "";
            DataTable dt = new DataTable();
            dt = (DataTable)ViewState["Remarks"];
            if (ViewState["Remarks"] != null)
            {
                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    if (hfnegativefeedback.Value == dt.Rows[i][0].ToString())
                    {
                        textbox1.Text = dt.Rows[i][1].ToString();
                    }
                }
            }

            ModalPopupExtender1.TargetControlID = SelectedDropdown.ToString();
            textbox1.Focus();
            ModalPopupExtender1.Show();
            Pnlnegativefeedback.Visible = true;
        }
        catch (Exception e2)
        {
 
        }
    }

when i select the poor from the dropdownlist panelpopup is displaying.
the panelpopup as follows.

NegativeFeedback

textbox1
ok(Button) cancel(Button)

in the textbox1 type the reason for poor and click the ok button. then selected dropdown and textbox1 reason as has been shown in gridview.

if suppose user want to click the Excellent in drodpdownlist, the poor reason has been removed in the gridview for that how can i do using csharp.


Regards,
Narasiman P