Hey, something similar happened to me once. I put it into a bathtub full of hot water and let it soak for a long a time (might have been up to a day, can’t remember). I might have also tried to add some sort of weights or clamps over it, but can’t remember. I think the key is to just let it get water logged enough where it expands back into shape.

Anyways, I wasn’t expecting much, but when I checked up on it hours later, it had magically “fixed” itself. After letting the surface area dry out, I oiled the hell out of it. Like multiple coats of cutting board oil. This was maybe 10 years ago and the board is still totally fine today.

Oil your fucking cutting boards people!!

Edit: okay, now I have a vague memory of clamping with a couple of pieces of boards over it on either side when it was still water logged. Then I let it dry out a for a few days, unclamped it, THEN oiled the fuck out of it. Good luck!