G'day Mike. Welcome to Apnea Board.
You don't need a prescription to purchase a CPAP in Australia so you haven't done anything wrong. As OpalRose said, get hold of the provider manual, which will show you how to adjust your machine. In the absence of a clinical recommendation, you can use the auto-titration feature of your machine to zero in on your best settings. I'd suggest you start with a minimum pressure of 6 or 7 and a max of 20. See how that goes and adjust from there. If you find it difficult exhaling against the pressure, use the RESlex feature which will drop the pressure while exhaling.
It's always best to use a software program to display the details of what your machine is doing. Unfortunately Oscar doesn't yet support BMC machines but you can download the BMC software from our private files forum:
http://www.apneaboard.com/forums/Forum-P...-and-Links
Alternatively BMC have a phone app, and a means of extracting the basic data via an on-screen code. I suggest you look at the manufacturer's site, which has a fair bit of detail.
https://bmedical.com.au/product/bmc-luna...-lcd-copy/
Best of luck!