I've recently came across an old banged up podhd 400 multi effect pedal, and I accidentally reversed the polarity while using a second hand power supply, does anyone know how to repair that kind of problem, I presume a thing like that would have some kind of major damage prevention?
What kind of problem? Reversing the polarity is a cause, not a symptom. Tell us what's wrong with it, if anything.

A decent protection circuit will prevent any damage so often all you have to do is plug it in correctly. 
Roc8995 the power supply has a changeable head and after a couple of uses I accidentally switched it the wrong way around, now the pedal doesn't turn on or do anything whatsoever, it is a digital pedal if that helps
Roc8995 yeah it did work perfectly well but after I switched the head around it just instantly stopped and it's. it turning on again
Probably cooked it with the wrong polarity.  Open it up and take a look around.  If there is a bunch of charred black stuff and it smells bad it is probably done.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY