I mistakenly added a harmony to the wrong track now that is marked with a big "H" even though I undid the harmony and the original audio file is there. Is there an easy way to revert the tracks type to "audio"?

The icon is changed using the right-click 'Category' function.

You can create your own icons under the User subcategory. It's a pretty cool feature once you learn it.
I've been known to take pics of musicians I record and use those for the icon, just for quick reference. Faster than reading the track info .. if I see an image of Barry holding a mic, I know it's a vocal track, if it's a picture of him with his sax, I know it's a sax track. I like this feature, and it's worth using on any project you plan to spend time on.