I dropped my iPhone 10 in bath but immediately got it out now it is dead. I thought it was water resistant

It is water resistant, but water resistant is not the same thing as waterproof. Having a little bit of water splash on the phone is different than dropping the phone in a tub full of water.

Take it to an Apple Store, let them have a look and they will explain your options.

Have you tried putting the iPhone inside uncooked rice , it soaks up the water pretty good , might work

That idea just ruins the rice.