Back camera does not work proper

If i zoom out, it is clear, but i cannot zoom in one bit, also the camera app crashes, also snapchat and other apps that require camera when I try to use it. Belive this is a problem on alot of these models. I have another one wich the camera works fine on but the sim card slots does not work. is it easier to change camera, or simcard holder on these phones? and what would be the most effecient approach in terms of teardown steps?