Once you’ve reached your destination, press Save Track to save it to your Captain’s Log. You’ll be prompted to give the track a name and description. Then press Save & Exit.
Within the Captain’s Log you can tap the Take Voyage icon and it will convert the track to a route that can then be used for a return trip or a future trip.
If you don’t want to save the track to your Captain’s Log, simply press Go Back and then Discard.