If you have blocked someone mistakenly or altered your mind about the block, however, it is likewise reversible. You can change your Personal privacy settings to unblock and permit somebody back into your Facebook world.
How Do I Unblock A Friend On Facebook
1. Click the down arrow next to "Account" on top right of any page on Facebook.
2. Click "Personal 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 beside the name of the person you desire to unclog. A list of individuals you have actually blocked is discovered under the Block Users area.
Idea
Uncloging somebody does not immediately put that person back in your friend list. You need to add the newly unblocked person as a friend 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 Do I Unblock A Friend On Facebook with your friends.