how to correct the bank reconcilation statement

This would require a modification to completely reverse an incorrect bank reconciliation but I would not recommend this as it would be much easier to do one of two things:
1) Revise the customers process - they are obviously missing a review process to make sure the reconciliation is correct before posting.
2) Create a second bank recociliation for the same date and posting any corrections needed, including new transactions to offset incorrectly cleared items. This would require two adjustments for the same item with opposite signs. Lets say you incorrectly cleared a check of $1,000.00, you would create a positive adjustment for $1,000.00 and a negative adjustment for $1,000.00 against the bank account using the same document number and posting date of the incorrectly cleared item. This has a net effect of zero in the bank account in NAV. You would make the balance per bank $1000.00, and clear the postive entry on the reconciliation. This will leave the -1000.00 entry open to be cleared on a subsequent reconciliation.