If you have actually blocked somebody inadvertently or changed 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 Can You Unblock Someone On Facebook
1. Click the down arrow beside "Account" on 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 "Unclog" link next to the name of the person you want to unclog. A list of individuals you have actually obstructed is discovered under the Block Users area.
Idea
Uncloging somebody does not instantly put that individual back in your friend list. You should add the freshly unblocked person as a good friend and wait on them to confirm the request.
And one more thing please don’t forget to share this awesome trick to use the How Can You Unblock Someone On Facebook with your friends.