As John said, it pops on and off.
You may be able to simply pop it back down, might require a bit of force. Just go sort of easy on it - the plastic clips that hold it in can be fairly fragile. See if you can look into the gap and see the clips to make it a bit easier.
Saying that, I took mine off and put it back on without breaking it and I'm pretty heavy handed.
These two YouTube videos might be some good;