How to run JS code after an Iframe form loaded and putting a custom value in the input?

http://dev.uniteconferencing.com/conference-account-sign-free/?pcode=25u50PT I'm trying to get the pcode value from url and put in the IFRAME form, I get the value using this code

jQuery(function(){
      var pcode = location.href;
      var pcode = pcode.split('=');
      var pcode = pcode[pcode.length - 1];
      console.log(pcode);

}); 

but when I try to put this value in the form’s promo code field here http://prntscr.com/dftezo , I can’t place this value because this form loads after loading every thing. I tried my best, using the boot , the bind , but not yet executed. please help. I am stuck in it from 2 days. Thanks