From the pictures it sort of looks like a wound. Is the spot raised like a wart or pimple? If it is a raised bump I really don't know what it is. I'm just trying to get more information so that maybe someone else can ID it for you.
I was hoping that someone else would give you some advice since I have never had a fish with that kind of lesion before. Here is my advice. I am guessing that the spot originated from a small injury which then became infected. I would start a routine of doing frequent water changes. Something along the lines of 30% or more per day. Monitor your water quality by using a liquid test kit. Check for Ammonia, Nitrite, and Nitrate. Ammonia and Nitrite should be zero. Nitrate should be around 20 PPM but even lower is better. Keep your Nitrate levels low by doing partial water changes. I would also add a dose of aquarium salt which should help the wound to heal. Dose the salt as directed on the package. You should increase the amount of salt slowly so you don't shock the fish. When you do water changes add the salt to the new water in the same ratio as the tank water. Also, if you are using tap water, you should add a water conditioner that neutralizes chloramines. Let me know how it goes or if you have any questions.
Cichlid salt is another product that I have never used. I suppose it would be ok but I'm not sure. When you add salt to the aquarium, it is best to dissolve it in water first. I mix it in a five gallon bucket and add it in when I do a water change.
Clean water low in nitrates will allow the wound (if that's what it is) to heal.
You can treat with Melafix which will reduce chances of an infection, however clean water will work also.
Keep an eye on the area for any increased redness or fuzzy white/gray growth which indicates a bacterial or fungal infection in which case I would treat with both Maracyn and Maracyn II.