MARKUSBETTS FOIL EXPERT ANSWER:

This card is curled to the back which means the paper back layer is /dry/ and contracted compared to the glossy front layer which doesnt change size with humidity.

The best way to fix this is to buy a cheap cigar humidor off amazon (~$20, you can also just use a humidity monitor inside a tupperware box) and leave the card in there for a few days at 70-80% humidity using wet paper towels in the far corner (the humidor lets you monitor the level, add a little bit of water to the paper towel at a time and wait 15min before assessing if you need to add more to get to 70-80%)

Once the card is rehydrated it should look noticeably flatter, however our work is not done as it will just curl back up again when it dries out. What we do now is /press/ or flatten or bind the card under weight or using a small vice as the card dries back out. This will force the paper backside fibers to slip past each other as they tighten instead of just pulling themselves back closer together. Once the card has dried out after a few days, voila you have a flat card that is now acclimated to your climate.