Open Spotify in the car. Go to Playlist and type in the name of your "unique" playlist name in the box. After, what seem and age, you should see the playlists below... However it didn't work for me, but I only have a free Spotify account so that may be the problem.
I did find Tesla Premium Audio however!
PS. Also it looks you can only save 17 songs or 2 playlist in the free Tesla Spotify account!