Hi @karibeary ,
As you know water and electronics and electricity are not a good mix.
The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the controller's operating design and could damage the components.
First do not connect or turn on your controller
Then you need to dis-assemble the controller and clean all the affected parts using Isopropyl Alcohol 90%+ (available from most pharmacies) to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is <70% IPA, can contain scents and is not as effective. If you do check the label to verify the amount
Here is a link that describes the process.
Electronics Water Damage
As always with electronics, especially surface mounted PCBs be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board.
Hopefully after you have done all this the controller might possibly work correctly again.
Here is a link to a video showing how to dis-assemble the controller, which may be of some help. (You probably don't need this as you've already opened it but it doesn't hurt to have a backup in case you forgot where a part goes when you re assemble it)
If this process seems too daunting, take your phone to a reputable, professional electronics repair service, experienced in water damage repair and ask for a quote for a repair.
If you decide to do this, do it sooner than later.