Map Gravity Forms Date Selector To Paypal Subscription

I use gravity forms on [login to view URL], I need to map the "date selector" to Paypal payments pro subscription "Start Date" So when a donor selects day to start donation, it tells paypal subscription to start the subscription on the selected date. My old developer sent me this: add_action(“gform_paypalpaymentspro_query_16”, “pre_submission_handler_2”); function pre_submission_handler_2($nvpreq){ if(isset($_COOKIE) && $_COOKIE[‘profiles_star_date’] == ‘’){ $date = $_COOKIE[‘profiles_star_date’]; $nvpreq .= ‘&PROFILESTARTDATE=‘.trim($date).’T00:00:00’; } return $nvpreq; } I'm not sure if it's right, and I don't know where to stick it. I already tried putting it in a few places with no luck.