If you have blocked somebody inadvertently or altered your mind about the block, however, it is likewise reversible. You can alter your Personal privacy settings to unclog and allow somebody back into your Facebook world.
What Happens When You Unblock Someone On Facebook
1. Click the down arrow beside "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 "Unblock" link beside the name of the person you want to unclog. A list of the people you have actually obstructed is discovered under the Block Users area.
Idea
Uncloging someone does not immediately put that person back in your friend list. You should add the recently unblocked individual as a good friend and wait for them to verify the demand.
And one more thing please don’t forget to share this awesome trick to use the What Happens When You Unblock Someone On Facebook with your friends.