To unlock a facebook application follow these simple steps:
1 - Login to your Facebook page.
2 - Click on where it says account (on the right side of the screen).
3 - Select "Privacy Settings."
4 - Once there, look down the option that says "Block List", click "Edit your lists."
5 - The following is a list of applications or people you''ve blocked, find the one you want to unblock and select this option (unlock) to the right of each application.
And that''s all, now you can have access to the application or profile''s people who had locked.