You can't really fix corrosion, because it tends to spread slowly throughout the device over time. It depends on what's damaged, if you're lucky it might only be the USB board which is cheap to replace, if it's components on the motherboard then replacing that is more expensive, if it's through the whole phone it might even be a bin job because it's probably going to continue to get worse over time.
Only way to know for sure is to take it to someone qualified (I.E a mobile repair shop) & have them take a look.
Edit - Or...You could replace the USB board yourself & see how that goes. It's easy/quick/cheap (~US$10) to do yourself, search for KeithRoss39's guide in General (search for 'replacing USB charger board' or similar), and if you're lucky this solves the problem. If it doesn't, then you take it someone qualified for diagnosis (and in changing the USB board, as you're pulling the phone apart, you'll be able to see if/how much corrosion is there).
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?