Health app. Tap “Browse”, tap “Activity”, tap “Workouts”, tap “Add Data” top-right. You can enter in the details (basically just changed it Functional Strength Training, enter the times, enter the calories you think you burned.
Not sure if it will sync to the other apps, though.
You can change the colors, the style of the time, whether it has seconds or not, whether it has ticks on the outside for seconds, elevation, or depth, and any of the complication slots. That is all you can modify.
It’s easily my favorite face these days. I think that it’s better than the old modular face.