Hey Ciaran,
Do you by any chance have a card clip? If not, send me a PM and I’ll send you a hidden link to a very cool one we plan to sell 🙂
If you already do, faro the cards face to face or back to face turning over 26 so they face each other. Put them in the box and in a clip and let them sit for a while.
This won’t fix a deck 100%, but it will at least flatten them out.
If possible, add 1/2/3/4 cards when done at the front and back of the deck so the clip is extra firm, if that makes sense 🙂
Let me know if this worked!
Cheers,
Aron