Salesforce: Salesforce Authenticator Re-Registration

Background: A Salesforce user uses Salesforce Authenticator for MFA; however, the account is removed by accident by mistake, or the app is deleted, or user has a new phone. So, when the user login to Salesforce, the user will get the following popup from the Salesforce Authenticator app. 

Solution: The admin can simply go to the user detail and disconnect "App Registration: Salesforce Authenticator".

Once disconnected, when user login again with username and password, the system will ask the user to add an Account in the Salesforce Authenticator.

Reference:

• Disconnect Salesforce Authenticator from a User’s Account