Here are some things that you should try (may need to do all):
- iron it (ensure to set it on to cotton setting - works with linen backed posters too)
- lie it down between the bed mattresses and have the
fattest heaviest person you can find lay in bed, that will add sufficient pressure to smooth it out
- turn the poster over face down and back over it, gently, a few times, with the car (you must ensure you align the tyre with the dink)
- spray the area of the dink with some common hairspray, with a quick burst. As it dries, it will tighten up the area.
- focus the suns rays thru a magnifying glass on to the dink. The heat will soften out the dink. I find about 70% focal energy clears out dinks, but be careful not more.
- on the reverse side, press a sharp knife point gently into the back of the dink. This will help to push the dink back into its normal position.
- lay the poster on a solid surface and press down on it with a clean toilet plunger. Stand each side and lift it up quickly without hesitation.