There are 2 functions in WordPress to let you display previous and next post links: previous_post_link and next_post_link. In general, they work so well and really save a bunch time when coding a theme.

Just need to add this code in theme functions.php file to make it work correctly.

https://codex.wordpress.org/Next_and_Previous_Links

Get the right prev/next post link when order posts by menu_order