I believe Garmin Connect web page is missing feature to add same pre-defined workout in multiple day's, at least I haven't found possibility for that.
So idea for developers (improve user expierence) - make it possible to add one workout to multiple day's without each time selecting again day when planned training should be held but to be able to select multiple day's and add one training to those days with one button click.
PS! AS-IS it is also possible to drag-drop pre-defined training directly in calendar view but trainings aren't displaied in UI in separate section, so when scrolling page down by trying to find proper traning, also calendar will change and it is not possible to drag-drop training somewhere in the end of workouts list into calendar