How to download kml file (Google earth file) on button click asp.netC#

Question

Hello I have created webfrom in asp.net on which user can upload kml file (Google earth file)..I have saved uploaded filein folder and file path in database.

Now on download button click I have to give same file for download

I got file path from database but I am unable to write code for download funcionality

Below is my download button click code :

protected void btndownloadkml_Click(object sender, EventArgs e) {
 con.Close();
 SqlCommand cmdkml = new SqlCommand("select * from FileMaster where ClientId='" + ddlclient.SelectedValue.ToString() + "' and FileType='KML' order by Srno DESC", con);
 con.Open();
 SqlDataReader sdrkml = cmdkml.ExecuteReader();
 if (sdrkml.HasRows) {
  sdrkml.Read();
  Response.ContentType = "application/vnd.google-earth.kml+xml";
  string s1 = sdrkml.GetValue(3).ToString();
  string s2 = sdrkml.GetValue(4).ToString();
  Response.AppendHeader("Content-Disposition", "attachment; filename=" + s2);
  Response.TransmitFile(Server.MapPath(s2));
  Response.End();
 }
}

please suggest changes