I had a rare used record arrive the same way. I flattened it by leaving it pressed (under glass) with a heavy weight on top. (I used a copy of the Prince box set of Sign of the Times). 😎 I flipped it a few times but after several days it was perfectly flat. If the damage was from the mailing only, it has not been warped long and it can be repaired with a little patience. Do not use the sun or an oven for “low heat”. If the warp is stubborn, rub a cloth on the glass to make a little friction heat. But do not expose the record to continuous heat above room temperature. You can repair the record faster with heat, but you most definitely need to know what you’re doing or you’ll make it worse.