you need your profile ID on facebook to do it. got your profile on FB you should see the follwing in the URL bar.
for example this is mine "http://www.facebook.com/profile.php?id=1293924117"
you need the bit I highlighted on yours, then goto your CP here, and then 'edit details' and paste that into the facebook section.
if you dont have that kind of ID, as above, you need the ID number in your URL, and add it to this profile.php?id="your number here"