When I want to ride a course with turn-by-turn, I will typically download a .fit file from RideWithGps and put it in the `NewFiles` folder on the Garmin. I can then usually access them by going to Navigation -> Courses.
However, this is no longer working for me. After downloading the files and safely disconnecting the device, the route does not appear in the Courses menu. No warning, error messages or anything. This put me in quite a bind.