Can’t disable 2FA for user

On our WPMU site there’s 2FA active for admins, all other groups are disabled. We now have a user who accidentially became admin for a few hours and did not set up 2FA, because we realized this was a mistake and set his previous group again.

But now 2FA remains required for this account although it is disabled for it’s group. How can I disable it again?

Regards,

Michael