Hi my ear was pierced using a gun, while piercing it had gone cross due to which I got a bump on my ear back side. Kindly suggest what can be done to reduce the problem

I am not sure what you mean by crossed. But to help the bump tea tree oil is usually very good for it. And never use the ear piercing cleaner they give you. Only slide the piercing back and forth in the shower when water is running on it.