To disable your iPhone, Apple Watch, or connected app on your Apple Health account as an activity tracker, you need to "un-allow" the Active for Good app to read your "Step" and "Active Energy" data from Apple's Health app.
How to disable (this is assuming you have the most updated version of the app):
- Open the Health app on your iOS device
- From the main "Health Data" screen, tap on the Sources tab
- Locate Active for Good and tap Turn All Categories Off
The next step is to add another tracker. See here how to do that.