I dont know why but mine came with admin admin changed to something, I dont know what. Bigpipe excellent customer service pointed me in the right direction to factory reset, here it is just in case somebody else either changes by mistake or has same issue

https://www.bigpipe.co.nz/faq/faq-hardware/faq-smart-modem/how-do-i-change-my-smart-modem-wifi-settings

Make and Model of new Fibre modem;

Arcadyan VRV9517