At some point soon we will do a simple reverse function, but that doesn’t help you now. 🙂 For now you can switch drawings around just by using cut/paste like this:
Click the thumbnail in the x-sheet you want to move, hit Ctrl X, then click where you want it and Ctrl V. Then do the same for the rest of the drawings you need to move. 🙂
It’s Cmd (not Ctrl) if you are on Mac.