Hi,
As you know liquids and electronics and electricity are not a good mix.
Any liquid causes corrosion and provides circuit paths for the electricity which were not in the tablet's operating design and could damage the components.
''First you need to '''remove the battery '''from the tablet.'' You may have to search on You Tube for videos on how to open your tablet. Even a video for a 'generic' brand of tablet may be useful if you cannot find one for your particular make and model. The sooner you remove the battery the less damage will be inflicted.
Then you need to dis-assemble the tablet and clean all the parts using Isopropyl Alcohol 90%+ to remove all traces of corrosion and in your case shampoo.
Here is a link that in general, describes the process.
[[Electronics Water Damage]]
You will probably have to replace the battery as it is very hard to recover a battery from liquid 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