It's actually super easy to solve and you don't need Snapshots. I'd guess that right now the delay isn't assigned to any footswitch at all. If you want the delay only on FS3 in stompbox mode you have to assign the delay to FS3 so it will toggle on and off along with the boost. Just navigate to the effect block and then touch and hold the FS3 footswitch and select the "merge" function to add it to the same footswitch as the boost. Should only take a second.