Let it sit for a while in a protected area off the ground so air can circulate around all sides. This is so moisture content can stabilize throughout the piece. This may take a few weeks for 1x stock, longer if thicker.
If after this the piece is still warped, I agree, that's the way it wants to be and there isn't much you can do about it.
If you do decide to plane it, wait until it is stabilized.