The first thing to do is roll them up again, as tightly as you can, in the other direction. You may find that will take all, or nearly all, of the curl out.
My personal habit is to fasten the plans of the model I'm working on to a sheet of foamcore, using staples. If you put them in the extreme corners, and take them out carefully when you're finished, the damage to the plans will be almost nil.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.