You can take the lens off and look through the viewfinder without a lens attached, if the problem still exists, then it’s the body. If not, it’s the lens. Nothing will be in focus, but you should have a full very of light without a lens attach.
Look through the front of the lens and make sure the aperture is open all the way, it’s possible it’s stuck or they didn’t put everything back together correctly. It should be open by default. If it’s stopped down even after the camera is turned on, then the lens is broken, or your contacts between the lens and the body aren’t functioning correctly.
Most likely an element got knocked loose during shipping.