Require re-register MFA, it should revoke Microsoft Authenticator app, not just phone numbers.
When revoking a users MFA sessions and requiring re-registration of MFA, AAD only removes the phone numbers from the users account. It does not remove the associated Authenticator app. There is no method to for a Global Admin to remove the Authenticator app association from the user. The only supported method is for the end user to log-in and remove it from the myprofile.microsoft.com page.
Robert Moir commented
Even if its just an option, we would like a way to revoke / delete old authenticator instances.