If you are only admin and if you can’t login with your admin account because of authenticator app, you will have to contact phone support team of Microsoft to reset verification process. https://support.microsoft.com/en-us/topic/customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
You may get some difficulties to get support from phone support team, because there will be automated system process during call. Call may hangs up or on hold, but admin user have to call several times. And they have to try phone number of different countries to get help security team of Microsoft.