anonymous user-8617, Only other way to get back access to the B2C tenant is to login with some other Global Admin account, who has the option to answer the MFA or who doesn't have a MFA setup. In case the user who is not able to login to the tenant, is the only Global Admin of the tenant, then there is no way you can delete the tenant. Until you are able to login to the tenant, you cannot delete that tenant.
For the existing user who is not able to login, you can try deleting the profile from the Authenticator app, and then trying login into aka.ms/mfasetup and try to create another profile in your authenticator app and then give it a try. Also, when you try to login to aka.ms/mfasetup, you would be promoted for MFA using the authenticator app, if that is set as your primary option, in that case, try to login using some other MFA option (secondary option) like using sms or otp in email and see by any chance if you can go around the authenticator option.