If you have actually blocked somebody accidentally or changed your mind about the block, however, it is likewise reversible. You can change your Personal privacy settings to unclog and enable someone back into your Facebook world.
How To Unblock Someone 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 beside the name of the person you wish to unclog. A list of the people you've blocked is found under the Block Users area.
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Unblocking someone does not instantly put that person back in your good friend list. You should include the recently unblocked person as a buddy and await them to confirm the demand.
And one more thing please don’t forget to share this awesome trick to use the How To Unblock Someone Facebook with your friends.