Thanks for posting in the Community, Mak,

If there's a change made on a previous reconciliation period, you'll have to undo the reconciliation to zero out the discrepancy. We'd recommend to run a reconciliation report. Here's how:

1. Click on the Reports tab.
2. On the search box type Reconciliation Report.
3. Click on Reconciliation Report.
4. Select the Account for the reconciliation report.
5. And choose a report period, then click View report.

You'll see any changes made from a previous reconciliation period. Then, to undo a reconciliation you need to do it per transaction in the Account history. Here's how:

1. Click on the Accounting tab.
2. Click on Chart of Accounts.
3. Locate the bank account, and click on Account history.
4. Click on the transaction needed to undo.
5. Locate and review the check column, locate the transaction with an R.
6. Keep selecting the checkbox until the box is blank to remove the R.
7. Click on Save.

You may want to check these article about bank reconciliation in QuickBooks Online:

• How do I view, print, or export a reconciliation report?
• Undo or remove transactions from reconciliations in QuickBooks Online

If you're not sure where the discrepancy came from, we'd recommend checking them with your accountant or bookkeeper to get more information to avoid messing up your books.

Drop a comment below if you need more help in QuickBooks Online. Have a nice day!