You need to fill the void created or it will slide back down, come freezing weather. Using a hammer and block of wood pound the post back down where it needs to be. Use your foot and press against the bottom of the post. Compact the ground as hard as possible. Plug the ends of rails that are inside the hinge or catch post.
Place rails in posts as per illustration.
Start with an 8 ft. piece for the middle rail and do the same procedure. The end result is that all the seams are not on the same post. Fill gate posts with concrete and rebar. Click here to see gate Picture. A small traffic cone with the nose cut off make a perfect funnel.