Hi @rebridge ,
As you know liquids and electronics and electricity are not a good mix.
The liquid 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 turn on your controller so as to minimize any further damage.
Then you need to dis-assemble the controller and clean all the affected parts using Isopropyl Alcohol 90%+ (available at most pharmacies) to remove all traces of corrosion and liquid. Do not use "rubbing alcohol" as in some cases this is only 70% or less, can contain scents and is not as effective. If you do have to use it, check the label to verify the amount of IPA.
Here's a link that in general 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 the ifixit guide(s) for repairing your controller.
Xbox One Elite Wireless Controller Series 1 (Model 1698)
If this process seems too daunting, take your controller to a reputable, professional electronics repair service, experienced in liquid damage repair and ask for a quote for a repair. If you decide to do this, do it sooner than later.