JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id='sampleXML' cols="50" rows="10">
    <settings>
 <application>
   <firstCase>PublicMonitor</firstCase>
        </application>
     </settings>
</textarea>
<div id='finalXML'></div>

JavaScript

$(document).ready(function(){
    var sampleXML = $('#sampleXML').val().trim();
    var xml = $.parseXML(sampleXML);
    
    $(xml).find('firstCase').each(function(){
        $(this).text('new value');
    });
    $('#finalXML').text(xmlToString(xml));
    console.log(xmlToString(xml));
});

function xmlToString(xmlData) { 

    var xmlString;
    //IE
    if (window.ActiveXObject){
        xmlString = xmlData.xml;
    }
    // code for Mozilla, Firefox, Opera, etc.
    else{
        xmlString = (new XMLSerializer()).serializeToString(xmlData);
    }
    return xmlString;
}