Is it possible to trim a workout from an Apple Watch?
Solution 1:
As of watchOS 4.0 and iOS 11.0 there is no way to adjust the length of a workout with Apple Watch or iPhone.
I experienced the same issue in the past and the only known way to do this is by
- creating an encrypted backup with iTunes and to
- edit the Health.app SQL database's entries
- Restore the backup to your iPhone.
You should let Apple know that this is a feature you want to see in future releases:
https://www.apple.com/feedback/watch.html