You tapped the “domain name.”
Everything to the right of the “@” sign is called the “domain name.” It is the name of the company that “runs” the email service being used.
The only way THAT changes is if you change the company that you choose for your email account.
BUT, everything to the LEFT of the “@” sign is called the “username.” And THAT is chosen by YOU when you sign up for an email account.
With that in mind, are you ready to sign up for an email account?