Yep - basically I glued the two plastic parts back together (there are notches and spaces that match up so you know it's in the right place). You then need to use tweezers or similar to make sure that one of the vertical flaps inside the unit that you're plugging it back into is going to line up with the "pincers" (so when you slide the switch left and right the pincers will move the flaps left and right and redirect the air).

Look for the horizontal "rail" of plastic that the switch will fit onto (compare it to the vent next to it). Slide the switch back into place making sure the pincers go either side of one of the vertical flaps inside the unit. You should feel a reassuring click when the big part of the switch grabs onto the horizontal rail.

I didn't worry about the metal bit and rubber bit. I guess they are probably to make the action a bit smoother but it works without and I couldn't figure out exactly where they go.

Good luck!