I could do it!...
The solution is to pause the training (go to Garmin Coach - then the three dots on the top right, choose "Pause"). Then resume it immediately and the missed training was there!... Hope…
I believe, you do not need to reschedule missed workouts of a coach plan. Simply pause or reschedule the future workouts, and start the missed workout directly on the watch:
Didn't work for me. Once it is marked skipped on the plan and your watch is synced, I can't move it on the calendar and I can't select it from the workplace. Also the work out plan progresses…