Custome Jquery is not working

Custom jquery code is not working, can you please help me?

What I want to achieve
If user selects first field second field becomes mandatory

jQuery(function($){

jQuery(document).ready(function(){
jQuery('#yith-wapo-6').change(function(){
    var index = this.selectedIndex;
      jQuery('#yith-wapo-7').prop('required', function(){
         return index == 1 || index == 2 || index == 3 || index == 4 || index == 5 || index == 6 || index == 7 || index == 8 || index == 9 || index == 10 || index == 11 || index == 13;
    });
});
    });
        });

The page I need help with: [log in to see the link]