This article explains how to change your X (formerly Twitter) username through your account settings, whether you're using X's desktop website or mobile apps for iOS and Android.
You can easily change your username or email address by pressing X in a web browser or via the mobile app.
To use X's website to create a new name, go to the More menu on the main page.
Go to twitter.com, log in to your account and select More from the menu on the left.