The only way to treat a pressure sores is to get the weight/pressure off of it. There are no creams or dressings that will heal it while pressure is cutting off the blood supply. I assume that it is on your bottom since you are in a wheelchair. Removing pressure from these sores requires bedrest, ideally including some time spent lying on your sides. Time up in your chair has to be very limited and the chair has to have a good quality pressure relief cushion such as a ROHO.
Staying in bed is a really hard thing for most of us who are hanging on to the closest thing to a normal day as we can. I have done it when pain signaled that a pressure spot was heading to become a pressure sore. (Finally found out that the problem was that I was getting to "broad in the beam" for my too small ROHO to be able to float me!)
Anyway, a few days now can prevent a lot of pain and weeks or months in bed trying to get an open wound to heal. They don't heal like a bad gash. The tissue is dead, not just cut open, and healing requires filling in the area with a large amount of scar tissue. Scar tissue is living tissue but in spite of its appearance and popular belief, it is not strong. Hopefully that is enough info and I don't have to go into the risk of infection or the loss of protein from a leaking sore. Or tell you stories of pressure sores I have seen on patients. Preventing those out comes is more than worth a few days in bed beginning immediately!!!
While you are lying there, ticked off by the whole business, decide if you need a better seat cushion, more pressure breaks by tilting and/or reclining, or someone to do pressure mapping to find if lateral supports of your trunk or a custom cushion is needed because you are sitting with your weight off center. Or maybe you are sitting on a seam of clothing that is the problem. Jeans are often thick seamed. Does your panty line correspond to position of the pressure area? Don't believe for one minute that the sore won't come back if you haven't corrected the cause.