The Health app takes similar data from different sources, like steps recorded from your iPhone and activity from your Apple Watch, and organizes it based on where it comes from. By default, Health prioritizes data in this order:

Health data that you enter manually. Data from your iPhone, iPod touch, and Apple Watch. Data from apps and Bluetooth devices.

When you add a new data source, it appears above all other apps and devices that contribute data in Health. You can change the order of sources at any time.