Shem Pepito I recognize this is an old question but because of the "interesting" answers I feel obliged to clear up some misconceptions. Rice does not work
Anytime you have any electronic device that gets submerged or immersed in any water, you have to clean it properly. The first thing is to not use the device, not turning it on or trying to charge it, to sync it or whatever else could supply power to the components. Remove the battery Then disassemble the device and clean each and every part with some high grade (90%+) isopropyl alcohol and a soft brush. This means every part, every connector etc. Rinse it a couple of times with the alcohol. It is okay to submerge parts in an alcohol bath. If there is gross contamination, use sterile water (not tap water) to clean that contamination of and then proceed with the alcohol. It is not necessarry to use any kind of air device to dry the board. Alcohol in a high concentration will evaporate quickly.
Once all the components are properly cleaned, it is vital that the battery gets replaced as well. Any battery that was exposed, will ultimately fail. After all that, reassemble the device (in your case the GoPro) and then evalaute for any issues. Until the device is cleaned you cannot do a proper trouble shooting.
Here are some good guides on how to clean things. This particular guide was written for an iphone but all the points apply to pretty much any device. Here is our greneral guide.
Even with all the meticulous cleaning there is still a high chance that the device will have some kind of issues. This is due to the fact that virtually any part can fail because of corrosion and shortcircuits. The better the cleaning, the greater the chance on fixing it. Ultrasonic cleaning would of course be optimal.
If you submerged your device and have nothing handy to work on it or cannot get to any tools etc., place the device in a plastic bag in clean water and place it in a fridge or other cool area. This will slow down the corrosion process until you can get the tools etc. to repair it.
Rice does not do anything