How do I unblock somebody from Facebook?

I accidentally blocked the wrong person on Facebook, that's just what I get for being so absent minded. This person's profile picture was the same as the person I was really going to block because they were both supporting the same thing with a flyer as their default. I didn't know that, and blocked the first person I saw with that picture until I noticed the name and felt really bad. I've been trying and trying to find this person again to unblock, but I can't seem to do it, of course, because he's blocked. Anyone know how to unblock? There should be a way...