We might be able to do it using a custom SQL statement. Please send an email to support and include the date that SHOULD have been used and the date that actually got used by mistake. Also whether it was all clubs or only a specific club that was affected.
We would have to modify all of the attendance records (Person_Session) and all of the Book and Section and Award and Visitor and Fee and Payment records. At least that is what I can think of off the top of my head.