Connecting Apple Health
Apple Health is switched on from the Runsei app on your iPhone (Profile → Connections → Apple Health); iOS asks which data to share.
What arrives. Your runs with distance, time and average heart rate, plus sleep, resting heart rate, HRV and weight. For a run Apple recorded with GPS (the Workout app on your Apple Watch or iPhone), the newest version of the app also reads the route, the heart-rate and pace series and, only when your watch recorded laps or intervals, the laps. Runsei never makes laps up: a run with no laps from your watch shows none.
What may be missing. A run another app (Garmin Connect, Strava, a third-party tracker) wrote into Apple Health arrives as a summary only. A treadmill or phone-in-pocket run has no route. An older app version sends the summary only. Until a run carries its own route, a connected Strava can supply it. Runsei keeps that Strava copy until Apple Health's own copy arrives.
Disconnect. Runs already imported stay; the permission itself lives in iOS Settings → Health.