Hi! To remove an account from the Microsoft Authenticator app, open the app, select the account you want to remove, then use the menu or settings option for that account and choose Remove account. The exact steps can vary slightly depending on your phone, but the option is usually inside the account details rather than on the main screen.
The most common reason you cannot get codes is that this installation of Microsoft Authenticator is no longer linked correctly to the account. This can happen if the app was removed from the account’s security settings, if the app was reinstalled, or if you changed devices without restoring the Authenticator backup. In that case, the app may look correct, but it is treated as a different installation and will no longer generate or receive codes for that account.