Hi
When a device is water damaged the best thing you can do is work fast!
So the first thing you are going to want to do is unplug the battery and completely dismantle the phone
Here’s a video guide you will need
[link|https://m.youtube.com/watch?v=LKyvP8x_IeY|https://m.youtube.com/watch?v=LKyvP8x_IeY|new_window=true]
Once fully dismantled you will want to clean off any corrosion with a soft toothbrush some cotton buds and some isopropyl alcohol
I would also help to have it taken to a reputable repair shop to have it put through a ultrasonic cleaning bath
If you have cleaned it and you still have no luck on getting it working have a look for any components that look damaged(burned ,cracked,loose,discoloured)as they could need replacing
Like I said if it sound like a lot or too much for you I would have it seen to by a professional as it will raise the chances of survival
Hopefully this helps
Any questions please ask
Thanks:-)