If needed, organization admins can reset a users 2-Way Authentication. To do this:

1. Go to SET UP > MORE > USERS
2. Select the gear on the left side of the screen next to the user you're trying to reset. 

3. Select "Reset 2-Way Auth" from the menu.

3. After reset, ask the user to sign in again and fill out the 2-way authentication form or press "Not Now" to set this up later.