Hi there CDS8,
Thanks for reaching out about your taxes. QuickBooks Online is a great tool able to help you keep track of taxes so you know the amount owed on your next filing. I can provide some information about adding, deleting or modifying a transaction in a previous filing period.
If you've marked a tax period as filed in QuickBooks Online, and add a transaction, delete one, or edit one, an exception will be created for the amount of tax modified to affect the next period. In this case, there will be an exception for the amount of tax that was on the invoice, that will automatically be reduced from this period.
Here's some more information about tax exceptions.
if you have any other questions, feel free to reach out here.