iPhone X waterproof???

The newer iPhone models are water-resistant, not water proof, If it was washed a few minutes ago, put it in rice ASAP. If it was less recent, your phone is gone.

After drying it, take it to Apple so that they can examine. They will tell you your alternative which will probably to replace it with an out of warranty replacement.

Rice is a myth. It will do nothing unless you leave it in rice in a sealed container such as a ziplock bag with the air evacuated from it for a week powered off. But leaving it powered off for a week will accomplish exactly the same thing.