AJAX :: Setting Label Using Modalpopup Selected Value?

I have a modalpopup control which has a gridview and search criteria. User selects a records and clicks modalpopup ok button ( which is set as modalpopup's okbutton). I have attached an event to okbutton click event. and inside this event, I am setting a label control which in on main page which called this modalpopup. I debugged code, it comes inside that event but doesnt set value. below is my event code.

protected void btnOkCustomers_Click(object sender, EventArgs e)
{
Int32 CustomerID = Convert.ToInt32(GridView2.SelectedDataKey.Value);
orders = new Orders();
DataSet CustomersDs = orders.GetCustomerById(CustomerID);
lblCustomerName.Text = "sadasdad"; // CustomersDs.Tables[0].Rows[0]["first_name"].ToString();
HyperLink2_ModalPopupExtender.Hide();
}