that is weird. I exported all the files and the whole project. Try to delete it and downlod again. I just checked the project from my side and everything looks fine.
on my end on unity i have a hierarchy under that is main camera with cube symbol, main menu controller with cube symbol, UI with cube symbol, audio controller with cube symbol, and scene changer with cube symbol. all of this is under hierarchy tab. when i click on audio controller with cube symbol under hierarchy it reveals the inspector and the gameplay tracks i can change and replace. inbetween hierarchy and inspector tabs in the middle of both of them is the project tab with a folder icon next to it. and under the project tab with folder icon is assets and inside assets is music and when i click on music in assets under project tab i can import songs import mp3 songs into the empty space. once it is put in empty space. i can then create new audio slide in gameplay tracks and put the song in there. that's how i can do it. does this help?