Water damaged, and returning, but cant turn it on to delete, and flash back

[machek]

So the phone is water damaged, wont even turn on or anything, had some screen power, but only minimal almost like a backlight but thats it. But I wanted to know how can I erase the info on it if I cant even access it? Secondly if the phone is damaged to this extent is it even refurbishable? Will they be able to eventually access it?