Wait! There's more! I did some testing.
Select your playlist in the mobile Spotify app and play it.
Now go to the C4 app and SELECT the large music icon (top left) of the music (the playlist you just started in the Spotify mobile app) that is currently playing in the room.
Look towards the right of the word Queue and select the 3 horizontal lines icon.
Save New Preset. Rename it if you wish and click "Go" on the pop up keyboard.\
Now click the Spotify icon in the C4 app and your preset should be there.
Select your preset and an option to Favorite To Room will be there.
Done.