JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="icon">filename_s.png</ul>

<ul class="icon">filename_s.png</ul>

JavaScript

window.onload = function yourFunction(){
    var str = document.getElementsByClassName('icon')[0].innerHTML;
    
    var res = str.replace(/_s\.png/g, ".png")
   
    document.getElementsByClassName('icon')[0].innerHTML = res;

    setTimeout(yourFunction, 5000);
}

yourFunction();