how to create method.....

i want to add new column in my database table like unique id (primary key ) when import excel file to a table then automatic generate new add column to a table (unique id ) following code:-

protected void btnUpload_Click(object sender, EventArgs e)
{
if (FileUpload1.HasFile)
{
string path = string.Concat((Server.MapPath("~/Data/" + FileUpload1.FileName)));
FileUpload1.PostedFile.SaveAs(path);
OleDbConnection OleDbcon = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;");

OleDbCommand cmd = new OleDbCommand("SELECT * FROM [Sheet3$]", OleDbcon);
OleDbDataAdapter objAdapter1 = new OleDbDataAdapter(cmd);

OleDbcon.Open();
DbDataReader dr = cmd.ExecuteReader();

string con_str = @"Data Source=vaio\sqlexpress;Initial Catalog=dbemp;Integrated Security=True";

// Bulk Copy to SQL Server
SqlBulkCopy bulkInsert = new SqlBulkCopy(con_str);
bulkInsert.DestinationTableName = "tbdata";
bulkInsert.WriteToServer(dr);
OleDbcon.Close();
Array.ForEach(Directory.GetFiles((Server.MapPath("~/Data/"))), File.Delete);
Label1.ForeColor = Color.Green;
Label1.Text = "successfully inserted";
FetchData();
newrow();

}
else
{
Label1.ForeColor = Color.Red;
Label1.Text = "Please select the File";
}
}
public void FetchData()
{
SqlConnection con = new SqlConnection(@"Data Source=vaio\sqlexpress;Initial Catalog=dbemp;Integrated Security=True");
SqlCommand cmd = new SqlCommand("select * from tbdata", con);
con.Open();
SqlDataReader rdr = cmd.ExecuteReader();
GridView1.DataSource = rdr;
GridView1.DataBind();

}
public void newrow()
{
SqlConnection con;
SqlDataAdapter dladpt;
DataSet dldst;
DataTable mydt;

con = new SqlConnection(@"Data Source=vaio\sqlexpress;Initial Catalog=dbemp;Integrated Security=True");
dladpt = new SqlDataAdapter("select * from tbdata", con);
dldst = new DataSet();
mydt = new DataTable();
dladpt.Fill(mydt);

DataColumn dcolColumn = new DataColumn("Link", typeof(string));
mydt.Columns.Add(dcolColumn);

DataRow drowItem;

foreach (DataRow row in mydt.Columns)
{
drowItem = mydt.NewRow();
drowItem["Link"] = "secret";
mydt.Rows.Add(drowItem);
}
GridView1.DataSource = mydt;
GridView1.DataBind();
}
}