Ah ah typical!

The particularity in Australia is that each Australian State issues their own Driver Licences.
I found some information about NSW here: https://www.rms.nsw.gov.au/roads/licence/visiting-moving/interstate-licence.html
You said that you have a licence condition A037 ('Auto motor bike only not exceed 125ml eng cap') therefore to be eligible to have the condition removed, you must satisfactorily complete a pre provisional rider training course.
Apparently there is also a rule on age (If you are over 30 you can go to an unrestricted licence and ride anything on two wheels) but you better double check.

For you friend, I found a full guide to which countries’ licences are recognised in Australia: https://austroads.com.au/drivers-and-vehicles/overseas-drivers/applying-for-a-license
But Namibia is not within the list unfortunately.