If you would like to reactivate someone's account who was previously deactivated, first go to the Users page and show the deactivated users.
Once the Deactivated option is selected, find the user you want to bring back. In this example, we want to reactivate Sal's account by pressing Edit next to his name.
Once inside the user profile, switch the account status from Deactivated back to Active.
Be sure to press Save at the bottom when you're finished.