As we can’t see it, we have no idea how bad or deep it is. All we can suggest is that you see a vet to ensure it doesn’t get infected. Cleaning with a saline (salt and water) solution.
How old are they? If they are young, then often they are fine as babies but once they hit 16 weeks of age and become teenagers is mostly when it goes wrong. there is never a very big chance of a boar quartet making it to adulthood together.
Do be aware that more than two boars together has a huge chance of failure. Its difficult to get the character match right in more than two boars, plus the space required to keep four boars together is huge - their cage wojld need to be 4 metres by 1 metre so if allows for one square metre per boar of territory. Anything less and they simply don’t have enough room each.
Now they have had a fight, then they will need to be kept separate permanently. Pairs of boars are best so if you can make two functioning boar pairs then thats good. A pair needs a cage of 180x60cm. Unfortunately when attempting a boar quartet what often happens after a fight is you end up with a functioning pair and two singles
The guides below will help further
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
A Comprehensive Guide to Guinea Pig Boars