Peplink Balance 20 Webpage address with IP forwarding

I am trying to use a Peplink Balance 20 router to extract a block of public IP addresses (/28) from an AT&T nvg589 modem giving me internet access via IP passthrough. When I set up the Peplink balance 20 with IP forwarding as per instructions the lan correctly presents me with the public IP addresses and I can no longer access the machine web page using it’s private lan address This was expected but I now want to access the web page via LAN/WAN but do not know the public address of balance 20 machine.

Any help here would be appreciated.