When you unblock someone, that person will be able to see your posts on Facebook that you share with the public. The person won’t automatically become your friend on Facebook. If you want to become friends with a person who you’ve unblocked, you’ll need to send them a friend request again.
To unblock someone:
Click in the top right of any Facebook page
Click Privacy Shortcuts
Click How do I stop someone from bothering me?
Click View All Blocked Users.
Click Unblock next to the name of the person you want to unblock.