Welcome to the Community, Alex. While there isn't an option to delete the GST group rate in QuickBooks Online, you can still remove it by making the wrongly configured GST group rate inactive.
Doing this ensures the rate won't show up in your GST dropdown menus and any existing transactions using that GST code will not be impacted.
To deactivate it, navigate to All apps > GST > Overview. Then, click the Settings dropdown, select Edit Rates and simply toggle off the rate you want to remove. For more details, you can check out this helpful article: Edit GST settings in QuickBooks Online.
Once the tax rates are deactivated, please note that there will be no changes in your existing transactions. To ensure your reports are accurate, you will need to manually go back and update any entries that were assigned the incorrect GST group rate.
If you have more further questions, please feel free to ask. We're here to help.
