Forwarding port settings, tcp/ip gaming

My room-mate wont leave me alone about trying to get his lucasarts game to work with multiplayer. we have a seimens router that uses NAT. we know what ports we need to open, but we cannot figure which numbers to put where so that it will allow us to run it. we have a number for one specific port, and then a range of ports, and we are unsure how to set them to the proper UDP / TCP assignments.

basically, if we have port xxxx, and range yyyy-zzzz, how do i make the router let me open these?

have all the necessary ports to open but need help as to where exactly to put them etc to host my clusterball game.
Any help much appreciated

Im not familiar with siemens routers but normally you’d just have to set the router to forward the ports to your room-mate’s IP