How to access the admin page for a router in IP passthrough mode with AT&T modem?

I have an AT&T Wi-Fi router with IP Passthrough Mode turned “on” so that I can have my TP-Link AC4000 device act as the network’s router.

On the AT&T Wi-Fi Router I went to “Firewall” and then “IP Passthrough” and configured it so that “Allocation Mode” was set to “Passthrough”, “Passthrough Mode” was set to “DHCPS-fixed”, and I entered my TP-Link WiFi router’s MAC address in “Passthrough Fixed MAC Address” field.

If I understand how this works this means traffic is passed to my TP-Link Wi-Fi router directly by the AT&T router and that my TP-Link Wi-Fi router now has the AT&T router’s public IP address.

If I am on my home network how do I access the TP-Link router’s admin page? Going to the public IP address does not work.