To reverse a reconciled bank transaction, you need to reverse the transaction associated with it. This will undo the reconciliation and release the bank transaction. 

Go to Financials > Bank Accounts and select the row of the relevant bank account. 

Select the Processed tab and use the Filter to search for transactions with a Reconciled status. A list of reconciled transactions displays.Locate the transaction using the Filter or search bar.

Open the transaction you want to reverse. Select ...More Options and then select Reverse. 

A window will appear confirming that you want to create a reverse transaction. The transaction type displayed will match the transaction type you are reversing. 

A reversal transaction is created, and the reconciliation to the bank transaction is released. The imported statement transaction can now be reconciled correctly. The transaction will be marked as a 'Reversal'.