I want to help you further with this GST concern, @roma3.
When the transactions are added in the program with incorrect taxes, the only way to update them is by manually changing the entry details one at a time. I know this is the tedious process, but it's the only way to correct them. Otherwise, you can undo them, and make sure to enter the correct GST component and then transfer it again to QuickBooks.
You might also want to reach out to a tax advisor to get help with correcting your GST. If you don't have one, we can help you find someone to help you. You can visit the following link to locate accountants based in Australia: https://quickbooks.intuit.com/au/find-a-proadvisor/#find-an-accountant
Please get in touch with us again if you need further with your transactions and taxes. You can use this thread anytime.