Need to do the opposite and manually add a workout data?
Here’show to add a workout to your Apple Watch.
How Do I Delete an Apple Watch Workout?

you’re free to’t actually delete the workout on the Apple Watch itself.
The Watch doesn’t have a feature to do that.
Here’s how:
On the iPhone, initiate the Fitness app.

TapShow Moreto browse workouts by months and by jot down until you find the one you want to delete.
Once you’ve tapped your choice, the workout is deleted.
How Do You Delete and Edit Workouts on Apple Watch?

That makes some sense.
You able, though, to delete workouts from thepre-installed iPhone Health app.
On theSummarytab, tapShow All Health Data.
TapWorkouts, about halfway down the screen.
Scroll down and tapShow All Data.
This screen lists every workout recorded in the Health app.
Browse it to find the workout(s) you want to delete.
To delete a workout, swipe from right to left across to reveal theDeletebutton.
(you’re able to also tapEditand then the red-icon.)
FAQ
Unfortunately, you might’t update a workout goal to a session in progress.
Then, selectCaloriesorTime, and then use the Digital Crown to set the limit.
Then, tapStartto get underway.
Go to theBrowsetab, and then selectActivity.
This setting blocks all screen inputs until you turn the Digital Crown.