If you're not looking to include all Users from a particular O365 Organisation, you can follow the steps below.
- Go to [Backups] > [Users]
- Next, simply find the particular O365 Organisation you'd like to exclude users from and click on the 3 dot icon.
At this point you will get 2 options;
[Disable Backups for this User]
Disabling Backups for this User will stop backups from taking place in the future. The Backup Data will remain available and can be restored from the Restore Wizards. You will still be charged a monthly fee for this User. This feature is useful to retain backups of a User that has been deleted or archived in Office 365. To re-enable backups in the future simply choose to 'Re-enable Backups for this User'
[Remove User from Subscription & Delete Backup Data]
Removing this User will stop backup and restore operations from taking place and delete all Backup Data. You will still be charged a monthly fee for this User. If you would like to Backup this User again in the future you can include it in your Subscription but older backup versions will not be available.