JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">
    Sometitle
    <div>
        <div>
            aa
        </div>
        <div>
            bb
        </div>
    </div>
</div>

JavaScript

var your_div = document.getElementById('header');
var text_to_change = your_div.childNodes[0];
text_to_change.nodeValue = 'new text';