AND before any diagnostics can begin you need the rest of the story. First thing, the forward facing camera works properly. Secondly, the FaceTime camera was preinstalled on the display assembly.
So before anything else can be done, the phone needs to come back in, screen password left so phone can be properly diagnosed. The original Camera from the original broken screen needs to be swapped for the existing camera and ensure all connections are good. Then and only then can there be a chance to diagnose the damage left by the heavy huffed horse if the problem still exists .
Note: could also be smug between lens and screen left from when screen was assembled at factory. Highly unlikely but would need phone to check.