I'm so sorry. Try using a paper towel and drying it first. Then use a screw driver to open it. If you cna open it after removing all of the screws try using a mini metal or plastic stick to put it in one of the sides of our tama and pulling the lid out.
Like Young Robot said, you can put it on the radiator over night and it might work but if it dosen't then I am afraid that your tamagotchi is broken forever. All I can say is never put any tamagotchis near water.
Well if you cant open it try letting it dry it a dry place thats not humid.. like ur house.
If happened to my cousen and she let it dry for a whil;e... yes a while. and Then it worked again a fter a day or so. But if you get lucky it will work but you wont see the butttons on the bottoms of your tamagotvchi when it works(hope fully it wont do that) :kusatchi:
If this doesnt help im so srry about the news and that i couldnt help