Here's the map if you push/remove the pile on the top left. I don't remember if that's where I got the air plate, but it'll give you a shortcut as you can see. The top middle is where you can place plates. Water will flood/fill the room where the ring at, earth will shake the ground, and air will help to swim to get the ring.
If I'm wrong, maybe it's on the other pile of junk. I don't know (forgot) where its located so just explore the second part of the junkyard.
Maybe it's here? I think is this where the other pile is.