How Do I Get Someone Back if I Blocked Them on Facebook?
Blocking another Facebook user means that you become invisible to her on the social networking site. She won't see you in search results, be able to read your comments on a mutual friend's wall or be on your friend list. If you have a change of heart after blocking a user, she is quickly removed from your block list, but not automatically added back to your friend list. After you unblock a former friend, she must agree to have a confirmed friendship once again.
Click on the "Account" link at the top right corner of any screen on Facebook. When the drop-down menu opens, click "Privacy Settings."
Scroll down to the bottom of the "Privacy Settings" menu. Click on the "Edit your lists" link in the "Block Lists" group.
Click on the "Unblock" link immediately to the right of a Facebook member's name in the "Block users" group. Click "Confirm" when prompted.
Point your browser to the Facebook member's profile. Use the search engine at the top of every screen on the site to find her by name, or click on her name on a mutual friend's profile to be directed to her profile.
Click the gray "Add Friend" button at the top of her profile, just to the right of her name. Once she approves your friend request, the user will be returned to your friend list.