If you are looking to replace the transaction please click here for the steps on how to do so.
Instead of replacing you could amend the transaction where you would be looking at going to the account history in order to edit the GST coding. To do so you can use the steps below:
Please note: In both cases if the total amount of the transaction changes from it's previous amount reconciled it will throw out the balance, so it's important it still matches the statement.
If the amount needs to be changed to reflect the bank statement, you will need to seek an accountant user to undo reconciliation report before relodging the period.