Editing reconciled transactions may result in discrepancies between your previous and next reconciliation balances. Before making any changes, I recommend contacting an accountant to help you manage the reconciled transaction so it doesn't mess up your books.
If you need to make changes to the transaction, follow these steps:
Go to Accounting.
Click on Chart of Accounts tab.
Choose the bank account, thenhit View register.
Look for the transactions and check if you can see R in the column.
Select the transaction and repeatedly click the R status until it's blank or unreconciled.