You can edit a posted line or transaction, to amend its Date, Details, Reference, Account, Tag, Tax or amounts.
Go to Banks > Bank Statements, and select the bank account.
Click Statement Batches.
Click the relevant batch, as per the example highlighted below.
Click the Edit button.
From there you can edit the Date, Details, Reference, Account, Tag, Tax, Payments and Receipts.
Double-click on the relevant column to edit it.