As you know, water and powered electronics don't mix, (unpowered is not that good either- powered is worse though). What you will have to do is disassemble your phone and look for any corrosion (usually coloured green or white and possibly furry) on the components and on the pcb.
You can try and gently brush away all the corrosion with a very soft toothbrush or a QTip dipped in isopropyl alcohol (90%+). Ensure that it is all gone. It may look like it if it is still moist from the alcohol but it may reappear once it dries so be aware of that.
Be sure not to brush/rub too vigorously as you don't want to lift the components off the board. Once you are sure that all the corrosion has been removed, - check both sides of the pcb and remove all the plug connectors from their respective sockets to ensure that there is none in there either, allow the phone to completely dry before reassembly.
Reinstall the battery (which should also be cleaned - be careful not to bridge the terminals) and hope for the best.
For future reference, if a phone gets wet, immersed in liquid etc, if possible, remove the battery as quick as you can. Removing the power can prevent a lot of problems occurring because water being a conductor can create undesirable electrical circuits which can and do damage components.
Unfortunately I cannot find a video which shows how to dis-assemble your phone so as to assist you further.