Hi,
The rice method is good but even better is to take it apart immediately and clean it directly using
Isopropyl Alcohol.
At this point you need to immediately take it apart and using a toothbrush with Isopropyl Alcohol
remove the corrosion. The corrosion will continue to happen and it will damage even further.
If the damage is just to the gold fingers you can always use a silver epoxy to fix it. I think there are some
gopro repair videos on this site. Just take a look at the videos and see if its something you can do.
All you need is time and patience.
After cleaning the unit you may be able to determine where the continuity has been broken or the area(s)
that are damaged.