As someone who ships a lot of paper products, it's bound to happen that someone receives a map with a crease or wrinkle in the paper. This happened just recently and I realized I should make a post I can easily point people to if needed. This method works for non-glossy paper and can often return paper to looking near perfect.
Step 1: Lay the paper on a dry, flat surface and smooth it out gently. If it's printed on, place the printed side down.
Step 2: Lay a thin cotton cloth over the paper. I love quilt squares for things like this.
Step 3: Lightly mist the cloth. If you're a bit nervous about adding too much water, you can mist the cloth off on the side and then lay it on the paper.
Step 4: On the lowest setting, heat up your clothing iron and gently iron the cloth first in the same direction as the crease for a few strokes, then across the crease for a few strokes. Repeat 2-3 times while applying light pressure. Never stop moving the iron once it's on the cloth.
Step 5: Remove the cloth and apply a heavy flat weight, such as books, over the crease for 24hrs.
That should do it!
For thicker paper such as for watercolors, you can apply the water directly to the paper but always keep a cloth between the iron & the paper to keep it from scorching.
NEVER use the steam function of your iron on paper. This may result in warping and more wrinkles.