Can I manage an Azure Active Directory (AD) guest user's multi-factor authentication (MFA)?

We have a guest user in our Azure Active Directory who has lost their mobile phone and is unable to sign-in using the multi-factored authentication. Is it possible for us, as admins of the Azure tenant, to manage their MFA settings?

We tried managing the user so that they would need to provide contact methods again (as per instructions at https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-userdevicesettings#require-users-to-provide-contact-methods-again), but the settings stated that MFA was disabled already.

What options do we have here?

Thanks in advance for any advice, much appreciated.