You can always navigate back in steps using the Back button or Return button on the remote. Such button may have a returning arrow on it.
Do you know the brand and model TV and/or model remote that they have? A picture of the remote may help where to press.
To change the on-screen username associated with entered Apple Account:
- From the sidebar in the Apple TV app, as found on the Home Screen of the app, navigate to Settings in that list.
- In Settings, go to Accounts.
- In Accounts, go to Edit Username.
(Any edits there only apply to the Apple TV app on this device. It is not editing the account itself.)
It is normal (default) for the user account to be represented with the first name of the user account in the upper left corner of the Home Screen inside the app. The default icon for that account is often the two significant initials in a circle, if no image is available for that account. Only in the Accounts section of the Settings of the app can one read the full email address.
Mistyped account credentials can be ignored by not finishing the entry and going back. Sign-in wouldn’t succeed for incorrectly spelled details anyway.
If the chaos warrants a reset (I doubt it), one can start over by resetting the Apple TV app, thereby removing any personal information and other customization. This wouldn’t alter the account(s). Reset is an option in the in-app Settings. You may need to scroll down a bit, as it is the 12th option in the Settings list on my TV.
To the same effect as a reset, one could delete and re-install the Apple TV app, but that may be even more work.
