In Workgroups DaVinci you have the ability to upgrade an anonymous user (a user who was previously added as a reviewer on a proof) to the collaborator user type.

To do so, click on your profile picture, select Account admin, and navigate to the Users tab.

Find the anonymous user that you would like to upgrade, click on the user menu, and select Upgrade user.

Click Yes on the upgrade user pop-up.

The user will be sent an email invitation to accept and set up their password.