How to import Apple Health data into another app
Short answer
For an ongoing import, install an app that supports HealthKit and allow it to read the health categories you choose. For a file transfer, use Export All Health Data in the Health app to create an XML archive. The receiving app must explicitly support either HealthKit access or that exported file format.
Connect an app through HealthKit
Start in the receiving app and follow its Health connection prompt. To review or change access later, open Health on iPhone, tap your profile picture, tap Apps under Privacy, choose the app, then enable the categories it should read.
Apple documents this path in Share your data in Health on iPhone. Access is category by category, so a sleep app may support sleep and heart rate without supporting every record in Health.
Export the complete Health archive
Open Health, tap Summary, tap your profile picture, then tap Export All Health Data. Choose where to save or share the resulting archive. Apple describes the health and fitness data inside as XML.
This is a broad file export, not a live sync. Before creating it, check the destination app's import documentation for Apple Health XML support. If the app only offers a HealthKit connection, use the permission route instead.
Fix a missing app or category
If the app is not listed under Health privacy settings, open the app and look for its Health connection first. Apple notes that an app that does not appear may not be compatible with Health.
If the app appears but a category is missing, the app may not have requested that data type. Reinstalling permissions cannot make an app read a category its integration does not support, so confirm the supported list with the app maker.
How Gyroscope does it
Apple Health and Apple Watch are Gyroscope's primary source. Gyroscope reads the full HealthKit set, including steps, workouts, heart rate, resting heart rate, HRV, blood oxygen, respiratory rate, body measurements, VO2 Max, glucose, sleep, mindful minutes, and dietary nutrients.
Direct integrations such as Oura, Garmin, Fitbit, Withings, and Strava can join the same timeline. Gyroscope deduplicates the merged records against your primary device.