How do I delete a workout on my series 8 iWatch?

Open the Apple Health app,tap on browse,then tap on activity,then tap on workouts,scroll to the bottom and tap show all data

Swipe left on the workout you want to delete and tap “Delete.”

The workout will be deleted, and the changes will sync back to your Apple Watch.

And in the fitness app tap on Workouts/Show More,then swipe left on the workout and tap delete.

I see that "delete a workout" is mentioned in this article:

Start a workout on Apple Watch - Apple Support

Hopefully this will help you out.