Root User MFA登録時エラーでログインできず

I understand you're having an issue with your AWS root user MFA. Based on your description, it seems you registered MFA with an unintended authentication app, and now you can't log in. You'd like to reset the MFA settings for your root user to get back to the initial QR code registration step.

If you're unable to access your root user account due to MFA authentication failure, you can try the following:

1. Use the "Sign in using alternative factors of authentication" option when signing in to your root account.

2. Follow the account recovery process, which typically involves:

• Email verification to the address associated with the root account
• Phone verification using the phone number associated with the account

If these methods don't work (for example, if you're getting errors during phone verification), you should contact AWS Support directly using the MFA device reset form. AWS has a specific process for handling root user MFA device issues.

For future reference, when setting up MFA, always ensure you're using the intended authentication app and verify the MFA is working correctly before completing the setup process.
Sources
Unable to login to root user(MFA autentication failue) | AWS re:Post
Root User MFA Access | AWS re:Post
Urgent: Root User MFA Issues - Cannot Access AWS Account Due to Invalid Contact Methods | AWS re:Post

以下のドキュメントの手順に従って、ルートユーザーの MFA デバイスを無効にしてみてはいかがでしょうか?
https://repost.aws/knowledge-center/reset-mfa-device

上記のドキュメントの手順を使用して MFA を無効にできない場合は、以下のフォームを使用して AWS に連絡することをお勧めします。
https://support.aws.amazon.com/#/contacts/one-support?formId=mfa