You can edit existing trails, but directly adding new ones is not intended. What you can do is create a GPS track, and then upload it with a note describing the problem.

I use the app Vesspucci for actual editing, it works well (but larger changes to OSM is a "full PC" kind of task). Notes from StreetComplete (from all users) show up on a TODO list in the app, so the more advanced users can decided on whether they want to create a node on the map from the note.