JSFiddle - React, Tailwind, and code Playground

HTML

<input value="30" class="NameX" name="ageeb[15].Name" />
    <br/>
    <input value="20" class="NameX" name="ageeb[5].Name" />
    <br/>
    <input value="10" class="NameX" name="ageeb[3].Name" />

JavaScript

$('.NameX').attr('name', function () {
  alert( this.name.replace(/^(.*?)\[.*?\]/, '$1[20]'));
});