How do you change the amount of your accounts closing balance for months that you did not use the program?

SUGGESTED

We started using Sage Business Cloud in October.  Prior to this we were using just spreadsheets for our accounting system.  When setting up the Sage program I was required to enter the year end date for our business which is a few months before we started to use the program.  I have added our accounts opening balance as of the end of the year as it would not allow me to do any other date in the opening balance.  So my question is am I able to somehow put the closing balance of each of the months that we did not have invoices or transactions for from May to September so that I am able to reconcile the account from September on?  or will I need to go in and add all of the transactions on the bank statements for all of the months from May to September to be able to reconcile properly for September?