Currently, there is not a way to add custom exercises to the Garmin Connect app. I use Excel to program for myself, and it works well, but it would be nice to have all of my health information on one app as well as have my workout on my watch. Due to there not being basic exercises such as Glute Ham Raise, Prone Leg Curl, Machine Chest Press, Ab Wheel Rollout, Weighted Sit-Ups, etc., I do not use the Garmin Connect app to program for myself.
Other than this issue, I love my watch and it's capabilities.
I have seen that this has been an issue for a few years, with many people requesting this feature previously. I would love to know when Garmin is going to roll this out.