Hi,
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 tablet’s operating design and could damage the components.
I’m glad that you didn’t put it in rice as this wouldn’t have helped anyway, because rice does nothing to fix the problems caused by corrosion.
Don't Put Your Device in Rice. Here's Why...
First do not turn on your tablet and then you need to remove the battery as soon as possible from the tablet to minimize any further damage.
Then you need to dis-assemble the rest of the tablet and clean all the affected parts using Isopropyl Alcohol 90%+ (available from electronic parts stores) to remove all traces of corrosion and water. Do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain scents and is not as effective. If you do use it, check the label to verify the amount of IPA. The higher the percentage the better
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 tablet might possibly work correctly again.
Here is a link to the ifixit Kindle Fire guide which maybe of some help.
If this process seems too daunting, take your tablet to a reputable, professional mobile phone 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.