I have bad news for you.
You cannot plug it in by USB. The TC can only be accessed over ethernet or wireless.
More bad news.. you don't have an ethernet port. You can buy a thunderbolt to ethernet adapter but that is not really great idea.
You can plug the TC to the main router.. tell us which one you have and I can likely help you since I am in Melbourne.
Set the TC into bridge mode and simply connect to it via the router you are using now for your NBN connection. There are some tricks involved in making it stable but it should still work.
Reset the TC to factory.. no files on the hard disk are lost.
Use airport utility to configure using short names, with no spaces and pure alphanumerics. Passwords with same rules but 8-20 characters. Just need to turn off its wifi which is easy once configured.
Please note if the laptop is running Catalina now.. a TC is not the greatest target for Time Machine.
I would recommend either using a different backup app, e.g. Carbon Copy Cloner.
Or I would buy a simple USB hard disk.. plug that into the MBP and use that. USB drive is faster, cheaper and more reliable than any other option.