how to add text after comma using C#

In datagridview record as follows

Name Mobileno Changes Message

GS xxxx C Dear GS, sep25(CL2)

I have one button when i click that button in datagridview records will be displayed. The datagridview code as follows

sql = "select message FROM Tb_Track_SCH where Fac_Code = '" + (DGV_Fac_SMS.Rows[i].Cells[0].Value.ToString().Trim()) + "' and Message = '" + (DGV_Fac_SMS.Rows[i].Cells[3].Value.ToString().Trim()) + "'";

oledr = GFun.ReadAcessSql(sql);

if (oledr.HasRows == false)

{

DGV_Fac_SMS[2, i].Value = "C";

}

I want to add Amended TT text after the , in the above datagridview.

When Changes 'C' is appear in the Datagridview i want to add Amended TT text.

I want output as follows

Name Mobileno Changes Message

GS xxxx C Dear GS,Amended TT sep25(CL2)

After comma in the datagridview how can i add the above Amended TT.

how can i do in asp.net using C#.