Welcome to the community.
You use your Netgear AC1900 Wi-Fi Router and connect it to our supplied modem/router.
You can simply disable the Wi-Fi of our supplied modem and connect your router.
Let me know how it will go and should you require further assistance.
I have tried couple of times to connect my tpg router by the use of netgear AC1900 wifi router but still couldn’t connect, please guide me, how can I resolve this issue. I didn’t resolve netgear router login issue by own then I visited this site https://www.netgearroutersupportnumber.com/ and got my solution.