This should do it for you.  This code populates the default value with the selectedindex.  Change the index to the specific option number you want.  

var JS_ControlName_X = JS_ControlName.replace('_hid',"");

NWF$('#'+JS_ControlName_X).prop('selectedIndex',0);

NWF$('#'+JS_ControlName_X).trigger("change");

I recently upgraded to the latest version of Nintex 2013, April 2024 release and discovered that using this code:

    var CurrencyRetrieved = NWF$('#' + ddlPaymentCurrency + ' option:contains(AUD - Australia Dollar)');
    var CurrencyValue = CurrencyRetrieved.val();
    CurrencyRetrieved.prop('selected', 'selected');
    NWF$("#" + ddlPaymentCurrency).parent().find('input').val(CurrencyValue);
    NWF.FormFiller.Functions.ProcessOnChange(NWF$("#" + ddlPaymentCurrency));

However when I use this code

var ddlPaymentCurrency = ddlPaymentCurrency.replace('_hid',"");
var CurrencyRetrieved = NWF$('#' + ddlPaymentCurrency + ' option:contains(AUD - Australia Dollar)');
var CurrencyValue = CurrencyRetrieved.val();
CurrencyRetrieved.prop('selected', 'selected');
NWF$("#" + ddlPaymentCurrency).parent().find('input').val(CurrencyValue);
NWF.FormFiller.Functions.ProcessOnChange(NWF$("#" + ddlPaymentCurrency));

it works. Can you explain why removing “-hid” from the control name JS declaration makes a difference?