
Do you want to update Information of tracks (that appear on rekordbox) in Device?
Or, want to update the metadata of the music file in Device?
Information of tracks in Device will be updated by exporting the track again.
But metadata in the music file won't be updated by exporting the track again because music file is only copied when exporting a track first time.
If you want to update the metadata of the music file, you need to delete the track from Device and export the track again.