Cant find how to mark the playlist to "Offlie sync"

[Robertkras4]

Put some songs to my playlist from my computer since they are not on Spotify. They work all fine on my computer but they are not showing on my Iphone spotify, same playlist. When I tried switching the listening device from my PC to Iphone with the song playing it showed this message (attached down below) saying to mark the playlist for "Offline Sync". So I followed every step in that message, connected to the same WIFI, turned off Firewall, launched spotify on both devices but now I'm stuck at the 3rd part saying to mark the playlist containing this song for Offline Sync since I can't really find the switch or how to mark it. SOMEONE HELP! I want to listen to my own songs that are not on spotify on my phone 😞