Add new device to the router

Hello 

This is my first time on this forum. I am working on setting up android media box for the friend so he can watch IPTV. This router has only one ROKU box hooked up wirelessly and his android box on ethernet cable. When I click on STBemu icon on Tv  it does usual thing (spinning arrow) and then nothing (not getting yellow loading Tv bar) . Box works at my place with the same internet provider but I am using rental modem/router. Logged in to the modem, all devices are active and appeared ready to work but can not get TV. Is there a way to setup android box by port designation or something else? (I am guessing)

Thank you for your help