Thanks for posting in the Community, Waynos,

We're unable to combine two QuickBooks Online accounts for BAS reporting. You will have to run two different BAS reports for each file and manually calculate the total amount due to be reported to the ATO.

Let's run the GST Detail report and export in QBO. Here's how:

1. Click on the GST tab.
2. Click on Run reports.
3. Click on GST Details.
4. Select a Report period, and click on Run report.
5. You can print or export the report for reference.

Check this link to learn more about: BAS Detail Report.

You can always post in the Community if you have other QBO concerns. I'll be around to help you.