WiFi Mesh Access Point LAN Port 1

How can I find the IP address of a device plugged into the lan port 1 on the WiFi mesh access point?

I need to configure my media server and I cannot access any advanced modem/mesh access point settings. I have spent hours googling and the instructions I do find do not work. I have a domain name I point to my media server to access my media files remotely.

Under connected devices it doesn’t even show any devices other than T-Mobile gateway and the mesh access point. 

Any help is greatly appreciated. 

Jason