How to change one selected option text to another select option text using jQuery

How to change one selected option text to another select option text using jQuery.

Firstly you need to get option text which you want to put on second selection select option text.

<script>
$(document).ready(function(){

   $("input.manual").on("click",function(){

   var dob_day = $("li.pms-field.register-dob select.day option:selected" ).text();
 var dob_month = $("li.pms-field.register-dob select.month option:selected" ).text();
 var dob_year = $("li.pms-field.register-dob select.year option:selected" ).text();

 $("li.pms-field.popup-dob select.day option:selected" ).text(dob_day);
 $("li.pms-field.popup-dob select.month option:selected" ).text(dob_month);
 $("li.pms-field.popup-dob select.year option:selected" ).text(dob_year);


        });
});
</script>