how to update values in a dropdown list from different table

on.Open();
string first_name = tb_first_name.Text;
string middle_name = tb_middle_name.Text;
string last_name = tb_last_name.Text;
string emp_group = ddl_emp_group_id.SelectedValue;
string emp_designation = ddl_emp_designation.SelectedValue;
int hrgroup_id = Convert.ToInt32(ddl_emp_group_id.SelectedValue);
int hrdesignation_id = Convert.ToInt32(ddl_emp_designation.SelectedValue);
string email_id = tb_email_id.Text;
string mobile_no = tb_mobile_no.Text;
string gender = rbl_gender.Text;
string login = tb_login.Text;
string synopsis = tb_synopsis.Text;
int hid = Convert.ToInt32(hidden_id.Value);
//String UpdateQuery = "Update hrEmpDetails set first_name=@first_name,middle_name=@middle_name,last_name=@last_name,email_id=@email_id,mobile_no=@mobile_no,gender=@gender,login=@login,synopsis=@synopsis where id =" + hid + ";";
String UpdateQuery = "Update hrEmpDetails set first_name='" + first_name + "', middle_name='" + middle_name + "',last_name='" + last_name + "',hrgroup_id=" + hrgroup_id + ",hrdesignation_id=" + hrdesignation_id + " ,email_id='" + email_id + "',mobile_no='" + mobile_no + "',gender='" + gender + "',login='" + login + "',synopsis='" + synopsis + "' where id =" + hid + ";";
SqlCommand cmd = new SqlCommand(UpdateQuery, con);

cmd.ExecuteNonQuery();
con.Close();