Contact Dell tech support and this statement from Dell explains the hinge policy.
Latitude 7420 has the same issue as the Latitude 5300 2-in-1 where the hinge comes away from the cover. Dell are aware there is an issue but Dell won't admit to users there is an issue. Where do I go to get this resolved? The laptop is still under warranty and has not been misused.
Latitude 7420, hinge mount failure