How to flatten the curl out of paper

flatten the print under a heavy weight

This is the easiest method and will work on a light curl.  Lay your print on a large flat surface;  place protective paper on top of the print;  cover it with a weight. The weight should be evenly distributed across the print. Leave the weight on for as long as a week for maximum effectiveness.

reverse wind your print

This is the more recommended option.   Take your print and lay it on a large, flat surface print side up.  Place protective paper on top of the print.   Carefully roll the print up so the image is on the inside. Take care that the rolling up is smooth. Use 3-4 wide rubber bands, placed at even intervals, to secure the print. Leave it rolled for 1 – 2 days, and as a rule of thumb,  the thicker the paper is, the longer you need to leave it.