You have a dropdown list, populated via sql data source, and you want it to have “Select a value” as the first selected option.
protected void DropDownList2_DataBound(object sender, EventArgs e)
       {
           DropDownList list = sender as DropDownList;
           if(list != null)
           {
               list.Items.Insert(0, "--Select Date--");
           }
       }