I also use Lightroom with my PC. I'm not much more than a beginner. Whenever I need help onre of the places I go is Youtube. This lesson seems to address your problem using a PC. Your Apple commands will have different names the process should be the same.
I hope this helps.
click here
TV has photo clubs and I have gone to some meetings. Go to a meeting and someone will help you. Go to Village activities for time and location.