1st select the 1st row details from gridview den use for loop to insert the into new table with additional information.
for(int i=0;i<gridview1.rows.count;i++)>
{
string num = GridView1.Rows[i].Cells[1].Text;
string staff_dept = GridView1.Rows[i].Cells[2].Text;
string str = "insert into intrmarks(VTUNO,dept)values('" + num + "','" + staff_dept + "')";
SqlCommand strCmd = new SqlCommand(str, con);
strCmd.ExecuteNonQuery();
}