How do I reconcile my account when the previous balance in Quicken Starter no longer matches the amo

If the reconciled opening balance has changed, a reconciled transaction has been added, modified, or deleted.  To determine the source of the change, I suggest you compare the running balance of the account register in the current Quicken file with the running balance of the account register from a Quicken file backup saved when the account was last reconciled.  One way to accomplish this is to print the registers to text files.