How to Unhide Things From Your Timelineby James Wright
If you accidentally hide a post on your Facebook Timeline or if you reject a post that you were tagged in, you can restore these posts from your Activity Log. Hidden posts are not deleted; they're saved in chronological order, and you can restore any of these posts to your Timeline if desired. This option is limited to posts on your own Timeline
Click on your name in the Facebook menu bar to view your profile, then click the "Activity Log" button in the lower right corner of your cover photo.
Click "Posts You've Hidden" on the left sidebar to display a list of all posts you've hidden and tags you've rejected. It make take a few seconds or more for the results to load, especially if you are looking for an older post made some time ago.
Click the icon of the circle and line beside the post you want to unhide and then select "Allowed on Timeline." The post is restored to your Timeline. It will be displayed in chronological order, not as a new update, so if you restore an old post, you'll have to scroll down through newer posts on your Timeline to find it.