User name or password doesn't work

Hello, OmSoZo.

As you've discovered, changing the name of a user account is not as simple as it sounds, and if done improperly may damage the account and prevent you from logging in.

Please familiarize yourself with the process and requirements before you make any further changes or attempt to reverse the changes you've already made.

Change the name of your macOS user account and home folder - Apple Support

If you can still login to an admin user account, you may be able to simply reverse the name change at the place you originally did the damage. Maybe.

do you mean you changed your user name and home folder name? to do that properly is extremely difficult. and if it is done improperly, you can be locked out of your mac and lose all data found in that user account.

this is the article that explains the process. Change the name of your macOS user account and home folder - Apple Support

if that is what you incorrectly tried to do, your only recourse will be to erase your disk and reinstall macOS from macOS Recovery.