I had a Franklin Mint offset litho print with heavy coclking along the top due to the tape they used. I laid the print face down on a flat surface covered with paper to keep the print clean. I placed a damp cloth over the area for a few minutes so it would absorb some moisture. Next, I placed a sheet of plexi on it, then stacked heavy books for a couple days. It reduced the waves, but not elliminated. The cockling was bad though. I don't endorse my method, but it worked for me. Perhaps a conservator can help?
BTW, this Franklin Mint picture had the worst framing. The top mat had no bevel and the bottom reveal was printed on the print itself and revealed 1/4" to look like the second mat! There was a piece of paper behind the print and cardboard behind that. The glazing was 1/16" flemsy plastic. I got it off ebay, and rematted and glazed it after fixing the waves.
John