Need to change the status wen i give ok button in dialog box.

I need to change the status of the Transaction, once the checkout button is clicked.

I created a dialog box on checkout button using clicked method as:

db = box::yesNo("Do you really want to checkout", dialogButton::Yes, "Checkout");
if (db == dialogButton::Yes)
{
// select forupdate axt
info( "We chose Yes");
}
else
if (db == dialogButton::No)
{
info( "We chose No");
}

But I don't know how to change the status of tat transaction, please help how to do tat.

Thanks in advance