First Go to your profile and click the arrow down above beside the small icons lock, globe, Chat and the friend request. Then click the setting as it shows on the picture.
And now you're on the other page you will see the red dot with the horizontal white line at the center saying the word Blocking so click that word.
After clicking the blocking you will manage the blocking now, here is the list where are the old times you block does people on facebook appear's and look the person you want to unblock now.
So I'm going to unblock Yobymmij lagnaraci. just don't afraid to click the link (word) UNBLOCK after the name stated.
Now you are asking here for your confirmation. And click CONFIRM
At this picture, Yobymmij lagnaraci are now gone on the list and you successfully unblock him/her.