How do you join a network on Facebook without adding the graduating year?

I know how to join a network, but I don't want to add my graduating year. I skipped this step when I joined, but now I can't seem to do it without my graduating year. Help!How do you join a network on Facebook without adding the graduating year?
Enter in something random. Then login ti facebook press profile and press edit profile. Then go under Education tab and erase your typed in info and press save.