Synching iPod nano (3rd Gen) files into Apple Music library

I rediscovered my iPod nano (3rd Gen) the other day and it works great and has a bunch of music I own but don't have through my current apple account. I am hoping to get my music off the iPod and into my current Apple Music Library on my MacBook, but every time I try to synch the libraries I get a notification that by synching libraries, all files currently on the iPod will be deleted, which is the opposite of what I'm trying to do. Any help would be greatly appreciated.