Hole in the head disease is curable. However, it's not an easy disease to clear up quickly, especially if your Oscar is suffering from a bad case of it. If possible, please post a photograph of your fish so we can see the severity of the disease.
Unfortunately, bad cases can lead to very bad scarring so that's something you have to bear in mind. The first thing you need to do is test your water for ammonia, nitrite, nitrate and pH. This disease is often brought on by poor water conditions. If you have any chance of curing your fish, you have got to keep your water and extremely good condition. What size is your tank? Also what kind of filtration have you got? In fact, please explain in detail what your set up consists of
Is the fish breathing heavily at all? Does it look like it wants to do eat when you put food in?
Anyway, I don't want to bombard you with too much information, I will only fry your brain. If you give us some answers and we will try and help you as much as possible