you can use setAttribute for this action

var i = document.querySelector("input");

i.setAttribute("name", "myinput");

ref: https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute

Supposing you have this 👇

<input type="text" value="23" id="age"> </input>

You can select that element by

const ageInput = document.getElementById('age');

If what you want is to change the text inside you can do this by

ageInput.innerHTML = "Hello World"

Or you can set a new attribute by

ageInput.setAttribute("refer", "true");

setAttribute documentation 👉 https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute