Regarding Face to Face - Add/remove attendees on Totara 2.2.15

I have a face to face activity setup in a course and I need the trainer to add learners to that session, they can do this by clicking on the [Add/remove attendees] link that's shown at the bottom of the session, however in the list of potential attendees are all the users on the site and not just the users in the course. 

I need the Trainer to be able to quickly add users from his course to that session and don't want him to be able to see all other users on the site.

Is this possible?

Regards

Bodo