I can lend a hand in recording your VAT payment in QuickBooks Online and have the wrong bank account changed.
To answer your question, yes, you can change the bank account used when recording the VAT payment in QuickBooks Online. You can delete and recreate the payment to change it to the correct bank.
Here's how:
Click Taxes in the left panel.
Go to the Payments tab.
Select the payment and click the drop-down arrow beside View.