How to fix my iPhone 4S camera?

I dropped my phone so I got a new back but the cameras still blurry how do I fix that?

It must be broke in differant way you did not give anoff info to tell what parts broke

Could be that the lens are dirty or has dust that got trapped inside
you need to be in a real dry and dust free room and use a clean, lint free cloth and carefully brush over the lens and check the lens in a bright light to see if it is really shiny before attaching back to the phone