Having had a nightmare with NBN first of all turning up to install at the wrong apartment THREE times because they failed to correct the wrong address on their computer, then refusing to work on ours because they didn’t have the authority and then installing the service on the worst of three lines into our flat (“because it kind of works and that’s all we need”), then refusing to change it because they can only afford to visit each property once, I’d say good luck with getting them to change anything.

That said, you could tell them that they installed the connection without proper authority and insist that they come and move it to where it should be.

But bear in mind that you are dealing with a huge monopoly with a massive bureaucracy and no accountability working through sub-contractors racing against the clock to get as much work done in as little time as possible – and you have an idea of the mountain you will have to climb to get anything done.

While you are waiting for them to come back and say “not possible” for the umpteenth time, investigate the possibility of getting a private contractor to do it at your own expense

Is it a fibre to the home connection, or is it using the existing copper telephone cable (“fibre to the node”)?

If it’s fibre, then my understanding is that it can only be moved by NBN Co. You log a request through your service provider. I have heard that under some circumstances, NBN Co will do one relocation at no charge, but take this with a grain of salt.

There’s a brief mention on page 11 of this document:
https://www.nbnco.com.au/content/dam/nbnco/documents/nbn-fibre-user-guide.pdf

If it’s copper, then any registered cabler can do the move and it shouldn’t cost much.

https://www.nbnco.com.au/learn-about-the-nbn/network-technology/fibre-to-the-node-explained-fttn.html