If you have actually blocked someone inadvertently or changed your mind about the block, however, it is likewise reversible. You can change your Personal privacy settings to unclog and allow somebody back into your Facebook world.
How To Unblock Somebody From Facebook
1. Click the down arrow beside "Account" at the leading right of any page on Facebook.
2. Click "Privacy Preferences" from the Account menu.
3. Click the "Edit Your Lists" link under the Block Lists heading. It is at the bottom center of the page.
4. Click the "Unclog" link next to the name of the individual you want to unclog. A list of the people you've blocked is found under the Block Users area.
Suggestion
Unblocking somebody does not automatically put that individual back in your good friend list. You need to add the freshly unblocked person as a buddy and wait on them to verify the request.
And one more thing please don’t forget to share this awesome trick to use the How To Unblock Somebody From Facebook with your friends.