I don't have any experience with the Real of Battle boards but they're plastic correct? Usual methods for reshaping plastic should work, heatgun and some pressure. A hair dryer can work if you don't have a heat gun.
A little even heat on the unpainted side and set if level on a flat surface and throw a text book or something else flat and heavy on the warped area. Let cool and it should be good to go.
Rinse and repeat if needed.
I would practice on something else first though to get a feel for the heat gun. You want it warm enough to fix the warpage but not so hot you'll melt all the detail. Go slow and be patient.
As far as storage I'd imagine keeping it stored flat and out of direct sunlight/heat should keep it from warping in the future unless you let Chaos play on it too much

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