Howto add mp3 files from an ext4 file system to the library?

Hi all,

I have a USB flash storage (128 GB capacity) drive with my music and the filesystem ext4.

The drive is recognized by lsusb and I can mount it by hand in a SSH session via the mount command, but how can I add the mp3 files from the drive to the volumio music library?

Thanks for any help.

Christian