Spotify "integration" into Service Planning is that for each song there is a special Spotify link (kind of like a link to a website) that tells your computer to open Spotify and play a specific song. If you click to edit a song, scroll down to the "Web" area, and enter the link to a Spotify song, you can save the changes.
Once a Spotify link is added, you will see the Spotify icon next to the song name in the list.
Updated