Export walk, hike, or bike as KML

I want to export a recorded hike or bike trip as a KML file. Is there anyway to do this?

I swear I did this once, but cannot remember how. I backed up my iPhone on my Mac, but do not know how to access the one bike trip I want.

I used to use a Garmin GPS to save and export hikes, etc. I see no reason to carry that device when I have a watch and iPhone acting as a recorder.