Please help so my kitten has had this red wound on his lip and a little inside

It's hard to see from this photo, but I think a vet visit is needed.

I agree with talkingpeanut about taking your cat to the vet. It is really hard to say what is going on from that photo.

 One of my cats had an allergic reaction to something and the inside of her lip swelled up and was red like that.  The vet gave her some sort of injection to stop the reaction and also cleaned the area.  This issue never happened again.

One of my friends had something similar to that picture show up on one of her cats.  It turned out to be a small cut that got infected.  The vet had to drain it and the cat got antibiotics.  Her vet thought it could have been from rough play since she has multiple cats.  The issue did resolve.

It could also be possible that your cat got bitten by something.

Any of these would require vet attention to be resolved.