Hi
Data can be deleted selectively using the Health app on your iPhone. For example:
- Go to the Health Data tab > Fitness > Stand Hours > Show All Data > Edit (upper-right) - then either tap on Delete All (upper-left) or delete individual data points by tapping on the minus sign next to them > when finished, tap Done (upper-right).
Alternatively, to remove all Health and Activity data from your iPhone, you can reset and partially restore your iPhone. Note that this involves the permanent loss of all sensitive data on your iPhone and watch, including Health data, HomeKit data, and saved passwords: