Can you convert an activity into a navigable course in Garmin Explore?

Haven’t looked in Garmin Explore but you can in Garmin Connect Interweb.

Yes you can. Sometimes activities might have too many points, and the maximum is 10000 per course. In that case, filter the points. Use Mapsource, Basecamp, gpsbabel or any other software that knows how to do it. When you have your activity’s gpx file with less than 10000 points, import it into Garmin connect as a course, and save the course. Your device will create and give you turn by turn instructions. 

Do you know specifically how I can import a track from Garmin Explore to my 5 Plus?  I converted an activity to a track, but I can't figure out how to access it on my watch.  Synchronizing in Explore or Connect don't copy it over.

This is the easy way to do it from Garmin Connect:

• Open the activity in Garmin Connect interweb.
• Click on the gear icon top right.
• Select Save as course - follow the prompts.
• Send to device.

I'm sure you can do this in Garmin Explore but this is easier and gives you a usable course without any need to mess around.

If I remember correctly you need to save it as a route in Garmin Explore not a track.