I use
https://zwofactory.com/ to make .zwo to load into zwift and do the workouts in that program. That site will also let you export workouts as erg or mrc files that can be used with various head units and likely also the phone app that some smart trainers have. I've used my bolt to run workouts on my kickr but it's not the most straightforward process. I am not sure how to do it on a garmin head unit since I don't have one anymore. I imagine most phone apps that come with a trainer have some way to use workout files but I've never used the wahoo app I have for my kickr.