Hi KylieD,

Thanks for posting in the Community!

In QuickBooks Online, once you've turned on the GST we're unable to turn them off. If you're not required to charge GST, you'll have to edit the transactions and set the tax code to Out of Scope. Here's how:

1. Click on the Sales tab.
2. Click on an invoice.
3. Click on Edit invoice.
4. Look for Amounts are field and set it to Out of scope GST.
5. Click on Save or Save and close.

Repeat the steps above for other transactions. Out of scope tax code will not be reported to your BAS report. 

Let's also set your Default tax code to Out of Scope in your Company settings. Here's how:

1. Click on the Gear Icon.
2. Click on Account and Settings.
3. Click on Advanced tab.
4. Locate Accounting tab, and set Default tax rate selection to Out of Scope of GST.
5. Click on Save.
6. Click on Done.

You can also check this link to learn more about: Simpler GST FAQ.

Keep me posted if you have other GST concerns or questions. I'll get back to help you the best that I can.