I uploaded some GPX tracks of hiking trails: how do I mark them as trails?
You typically have to load them in the editor of your chose and redraw or trace them. While you do that, you can correct all errors. With errors, I mean position recordings that look way off. This is more likely to happen near high buildings or in canyons or when you stand still for a while.
Then add the necessary tags to the newly drawn way. Typically highway=path or footway or track. Please also add surface and perhaps sac_scale, smoothness and width.
I’d include trail_visibility in that list of additional tags. But at an absolute minimum, please put a surface tag on it.