How do I set my default Music folder? [duplicate]

I recently moved all my music to a separate partion, moved ~/Music to ~/Music-bak and symlinked a new Music directory to the partition.

Nautilus updated the bookmarks to show "Music-Bak" under Computer. How do I tell it that "Music" is my real music folder?

As you mentioned, when you modify (rename / move) Music folder it will point to the new folder.
To force it to point to a different folder, modify file ~/.config/user-dirs.dirs (it's a text file) and set the XDG_MUSIC_DIR parameter to point to your Music.

One can restart GNOME by pressing Alt + F2 together and
entering restart as the command, committed by the ⏎ key.

Or use ubuntu tweak

You download it from here : http://ubuntu-tweak.com/