If you have blocked someone inadvertently or changed your mind about the block, though, it is likewise reversible. You can alter your Privacy settings to unclog and permit somebody back into your Facebook world.
How To Unblock Facebook Friends
1. Click the down arrow next to "Account" at the leading 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 individual you want to unblock. A list of the individuals you've blocked is found under the Block Users section.
Idea
Uncloging somebody does not immediately put that person back in your good friend list. You must add the newly unblocked individual as a pal and wait for them to verify the request.
And one more thing please don’t forget to share this awesome trick to use the How To Unblock Facebook Friends with your friends.