Stashu,
Sorry, I thought the elevator was just bare wood. To use the first tip that I gave you will need to strip the monokote off for that to work. There is something else you can try first before you go to the extreme of stripping the covering off. Use a heat iron (the same that is used for covering) and use it to heat the elevator. Put the elevator on a flat surface and heat it. You'll want heat that is a little below the temp that the covering shrinks at. Heat the elevator and press down on the warp at the same time. You'll have to work on it for a bit because it won't happen immediately, if it does help. Keep this up until you can't get the warp to change anymore, or you have removed the warp. If that doesn't help then go to the first tip I posted.

Hope this helps

Ken