P780 - Rear camera not working

Hello, The rear camera of my lenovo doesn't work. It is model 2014 and after downgrade from kit-kat it just stops. I saw in some forums, that I have to change the apk file for the camera, but can't do it. Nothing happens when I install it normaly. Some say, that it has to be instalet via total comander or recovery consol. But I don't know how to do that. Any ideas?
S136 stock rom.