You can save exercises to your exercise library so you can save time creating future workouts.
To do so, just open the more menu next to the exercise library and click "Add to exercise library".
You can also add exercises directly to the exercise library by clicking the explore menu in the top corner of the editor, and navigating to the "Exercise library" section.
From there you can update/delete existing exercises from your library, or add new ones.
Here's a quick demo of how this works: