I did it myself but I'll explain. You'd go to the set page and click the See Any Inaccuracies button, and then select wrong missing notes. You'd then go to that IR, (I just use the redirect button to make it easier, and click tools. Then choose under set, Update Notes. It'll take you to the set, (if you have the permissions,) and you would choose Add/Append, and then type the note you want and then use the drop down to choose from which card to which card gets this note. Maybe someone else can explain it better and with photos but that's how I did it.
Thanks - TwinKiller. (Luke)