To reset a user's multi-factor authentication (MFA) connection, do the following:
Log in with an administrator account
Click the Settings gear icon, then click Setup
Type "users" in the Quick Find box, then click Users
Select the user from the list
Review the fields for App Registration, Security Key (U2F), Lightning Login, and One-Time Password Authenticator
Click "Disconnect" next to each authentication method to reset or remove
After resetting a user's MFA, they will need to log out and log back in to Salesforce. When they log back in, they will be prompted to set up a new authenticator.