With the new update the possibility to edit or send a workout through garmin connect is no more possible.
The buttons are simply no more there.(see screenshot, the action buttons are missing)
I hope that you will fix this regression. 
Any problems need to be reported to the Support: https://support.garmin.com
However, as I wrote, the app v4.39 still allows editing of Workouts, so as I advised, you should first try clearing the cache of the app or reinstalling it. Apparently your installation is somehow broken.