This guide will explain how to join a user to several sub-domains quickly without using drag and drop.
- Click on the user you want to join to the sub-domains
- Click the the tab "Joined Domains" on the right side

- Click on the "chain" icon to see all sub-domains.

- Click the button next to the sub-domain you wish for the user to join.

- Click the green "Checkmark" button to save the changes.

- The user is now a member of all checkmarked sub-domains.