Only a Workspace Administrator can reset the MFA Settings on a users account.
Users are presented with a "Change authentication method" option when entering either their SMS or Mobile Authenticator code as below:
If they select this they will see the message below informing that an administrator will need to do this. Clicking the blue 'administrator' link should provide them with their administrators email address.
How can an admin change this?
For an admin to change this they will need to browse to Admin Tools -> Users/Groups -> Manage Enrolled User and Group permissions. Navigate to the user a select the shield icon highlighted below:
Clicking this icon will prompt the admin to confirm the MFA Setting reset for that user. The user will then start again by being able to select an authentication method.