I am unable to get row index

Question

my gridview and added a  modal popup like this to view users details

when i click on the approved button inside the modalpopup  the status column in the grid must be changed to "Activated "  .

present value in that column is "success"

here i am trying to get the selected row value from inside popupmodal i am unable to catch the row index pls help me i dont know what to do 

protected void lbtnApprove_Click(object sender, EventArgs e)
{
    try
    {
       // BankList list = new BankList();
        GridViewRow selectedRow = grdvwMerchantBanks.SelectedRow;
        long id = list.BeneficiaryID;
        if (selectedRow != null && long.TryParse(selectedRow.Cells[0].Text, out id))
        {
            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
            {
                con.Open();
                SqlCommand cmd = new SqlCommand("UPDATE BeneficiaryDetails SET Status = 'Activated' WHERE BeneficiaryID = @BeneficiaryID", con);
                cmd.Parameters.AddWithValue("@Beneficiary", id);
                cmd.ExecuteNonQuery();
                con.Close();
            }
            selectedRow.Cells[1].Text = "Activated";
           // lblSuccessMessage.Text = "Beneficiary Approved Successfully";
        }
        else
        {
            //lblErrorMessage.Text = "Please select a beneficiary";
        }
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

 

my db   i"ve taken identity for beneficiaryid

ALTER procedure [dbo].[usp_InsertMerchantBanks]
(
	@BeneficiaryID				bigint,
	@BeneficiaryCode			nvarchar(200)='' ,
	@BankName					nvarchar(250) ,
	@IFSC						nvarchar(80) ,
	@AccountNumber				nvarchar(200) ,
	@BeneficiaryName			nvarchar(200) ,
	@TransactionStatus			nvarchar(200)='',
	@Userid						int='' ,
	@APIPartnerID				int='' ,
	@NameAsPerBank				nvarchar(200)='' ,
	@Validated					bit ='',
	@AccVerifyTransactionID		nvarchar(200)='' ,
	@Status					    nvarchar(200) ='',
	@CreatedDatetime			datetime ='',
	@username					nvarchar(200)='' 
)
AS BEGIN
begin try
if(@BeneficiaryID=0)
INSERT INTO MerchantBanks VALUES
(		
	@BeneficiaryCode			,
	@BankName					,
	@IFSC						,
	@AccountNumber				,
	@BeneficiaryName			,
	@TransactionStatus			,
	@Userid						,
	@APIPartnerID				,
	@NameAsPerBank				,
	@Validated					,
	@AccVerifyTransactionID		,
	@Status					    ,
	@CreatedDatetime			,
	@username
)
end