How best to plan a 5K on a map for training?

This depends upon age and location, but when I was training for a 10k about nine years ago I just trained on a treadmill. I was in my late 30s then and at a location where I had no asthma symptoms. I just ran at a 8min/mile pace with a 2.5deg incline. A 10k would take 50mins to complete.

It took me several months to get there of pushing out my run distance a little bit longer day by day, but I was always on the treadmill for an hour. If I could only run for 20mins then next 40mins we’re walking. The walking pace was dictated by heart rate trying to keep my heart rate at around 150bpm. The long walks burned more fat than the runs and built out my leg muscles.

One I was able to get to a 50min 10K I found I was surprisingly close to a 20min 5k or a 12min 2mile. When I ran in a real 10k I did in under 48minutes on a course with many steep hills.

5K - a long-distance road running competition

https://onthegomap.com/ is quite good for sharing routes.

If you want it on your preferred fitness device you'll need to use something it supports. Generally most places can import a GPX file https://en.wikipedia.org/wiki/GPS_Exchange_Format