Unlock the phone and open the Camera app.

Test the camera by making sure that it focuses properly and there is no visible residue left on the lens.

If the rear-facing camera continues to have trouble focusing, continue carefully removing glass shards from the camera cover.

If you have removed all glass shards and the camera still does not focus properly, the lens may be scratched. Use the iPhone 7 Rear Camera replacement guide to replace the phone's rear-facing camera.