Merge Activities recorded with several Garmin devices

I would like to merge activities recorded with more than one Garmin device.

Example: Cycling recorded with Edge 520 and at the same time as C<cling with Fenix 5s. Would love, if the same activities at the same time would automatically be merged. This would allow to record the heart rate with the Fenix 5s and include it in the cycling recording of the Edge 520.

Currently it appears as if I had made 2 times the same activity at the same time on the same track.

Any help, ideas.