There are various YouTube videos which can assist with this issue and you can try the options below, though if you are at all unsure you should visit the nearest apple store or phone provider store to ask them to diagnose the problem as your camera lens may have been damaged/dislodged or you may have a configuration issue.
1. go to settings/general and see if a pop-up message appears warning of any issue - you may need to visit an apple store or phone provider store to resolve
2. go to settings/camera/record video and turn on enhanced stabilisation
3. go to settings/shut down - your phone may simply need a reboot
Example of a partial document view: -
