If you have a user that is having issues logging in with MFA, Require Re-register MFA will make it so that when the user signs in next time, they will be requested to setup a new MFA authentication method.
As an administrator assigned the Authentication Administrator or a Global Administrator role you can require users to re-register for MFA. This is a good first step when troubleshooting Multi-Factor Authentication end user issues.
- Sign in to the Azure portal.
- On the left, select Azure Active Directory > Users > All Users
- Choose the user you wish to perform an action on and select Authentication Methods.
- Click Require re-register MFA and save.
The user will now be prompted to setup up MFA again on next sign in.