Go to AGENTS / MAILBOXES agents and click on the bulk add button.
On the next page, click on the bulk add agents button under the Microsoft Office 365 option.
You will be redirected to an o365 login page. Sign in using a super admin account and accept the permissions.
You will be redirected back to TTR where you will see a list of all of your mailboxes. Tick the mailboxes you want to add to TTR and click save agents.