As u dont have access to the app anymore, the only way to resolve this is to request for Product Support to reset MFA for the affected user for microsoft accounts. Contact Product Support with the email address for the affected user. https://azure.microsoft.com/en-us/support/create-ticket
If you have other accounts e.g socials you need to contact their support teams
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,