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 (or a user with a license and privileged administrator role) 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