Default workout setting on Health app

There is no default workout setting in the Health app on your iPhone. The Health app displays whatever "workout" data that was synced to it (or entered manually) as a "Workout".

Are you perhaps asking about the Workout app on the Watch? It also doesn't have any "default" app that I know of.

Ah, I see what you mean. I rarely add manual workouts. I don't see any way to change that. You can let Apple know your thoughts here:

Product Feedback - Apple

Actually, there IS a default setting for workouts in the Health app. When you manually create a new workout, it always defaults to "Running"...

Every time I create an Elliptical Workout, I have to scroll all the way from R to E. It's very irritating.