Hiii,

Below script working fine for us.

Many thanks to @Ankur Bawiskar  and  @Allen Andreas .

Client script:

function onChange(control, oldValue, newValue, isLoading) {
var headers = g_form.getControl('u_region').parentElement.querySelectorAll('.col-xs-4');
 var collectorName = 'u_region';
var filterString = '';    
    if(newValue == 'Australia'){
        filterString = 'question.nameSTARTSWITHu_region^textNOT LIKEAustralia';
    }
    else if(newValue == 'Austria')
    {
        filterString = 'question.nameSTARTSWITHu_region^textNOT LIKEAustria';    
    }

    setCollectorFilter();
    
function setCollectorFilter()
{
//If it hasn't rendered yet, wait 100ms and try again.
if(typeof(window[collectorName + 'g_filter']) == 'undefined')
{
setTimeout(setCollectorFilter, 50);
return;
}
//Reset the filter query
window[collectorName + 'g_filter'].reset();  
window[collectorName + 'g_filter'].setQuery(filterString);  
window[collectorName + 'acRequest'](null);  
//Redisplay the list collector variable
//g_form.setDisplay(collectorName,true);
    
}

   
}