If you have actually blocked somebody accidentally or altered your mind about the block, however, it is also reversible. You can alter your Privacy settings to unblock and allow someone back into your Facebook world.
How To Unblock People From Facebook
1. Click the down arrow next to "Account" at the top 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 "Unblock" link beside the name of the individual you desire to unblock. A list of individuals you have actually obstructed is found under the Block Users area.
Pointer
Uncloging someone does not instantly put that individual back in your friend list. You need to add the recently unblocked person as a pal and await them to validate the request.
And one more thing please don’t forget to share this awesome trick to use the How To Unblock People From Facebook with your friends.