Welcome to the community!
It will depend on what modem/router from your NBN service you have. Can let us know what brand and model number of modem/router from NBN you have?
I'll be waiting for your response.
You can try to follow this simple step to setup your Huawei HG659 to ADSL2+ service.
Step 2. Step 3. Step 4.
Hope this help.
Let me know how it will go.
Please be advised that supplied HG659 does not support ADSL configuration, it is intended for deployment on FTTB (VDSL) or NBN connections only.