Apple Watch activity too high
You should be able to delete the data relating to this via the Health app on your iPhone.

More specifically:


On your iPhone open the Health app
Tap on the Sources icon at bottom
At the bottom of the Sources screen you'll see a list of your devices - one of them will be for your Apple Watch. Tap on this.
Now you'll see a range of options - tap on the one that says Exercise Minutes
Now you'll see a screen that lists all recorded data, sorted with most recent at top
Identify the one(s) you need to delete
Now tap on the red Edit option at top right
Now you can delete any of the entries you want to (NOTE: Be careful not to tap on the Delete All option at top left!)