Touch screen doesn't work after the phone got water in it

Yesterday, I dipped the upper half of my phone to record a short underwater video (in fresh water, not salt water). Soon after, the phone died and wouldn't turn on. I figured out that the backdoor glue was not strong and so the water seeped into the inside of the phone (as a context, my phone was repaired at a Samsung Service Centre a year ago). As the backdoor was loose, I could easily open it without any tool, so I did. I tried to airdry the phone for half a day.

That night, I tried turning it on again, and it turned on. But the touch screen doesn't work at all. Now I can't even turn it off because the touch screen doesn't respond to anything. What should I do now?

Please help, thank you very much!