Provide a second or third way to do 2 factor authentication, which can be used in case the originally set up authentictor app can’t be used anymore (phone broken, lost, app deleted).
Usually systems with 2 factor authentication not only use a single way to authenticate with a code generating app. Instead the user can provide a different email address or a phone number to receive a code for 2fa when the authenticator app can’t be used.
Users are locked out of web.nuki.io when the authenticator app can’t be used anymore.
Dropbox 2FA allows using different ways to authenticate