Usually your router will have a "Client List" when you log in to it. The list will show all of the IP addresses connected to your network and each client's MAC Address. If you check your network settings on your xbox you should be able to find your xbox's MAC Address, which you can then match with an IP address listed on your router. If that doesn't work, you may be able to find your xbox's IP address listed under your xbox's network settings as well, but I'm not 100% sure about that.
You need to login to your router. Usually that is by typing something like 192.168.0.1 into your web browser. Each router is different, but mine had an option under "Setup" for DMZ. Then I just typed in my xbox's IP address. Try looking up your own specific router model online and search for how to set up a Demilitarized Zone (DMZ) on it because I'm sure yours probably isn't the same as mine. If you have any other questions just let me know and I'll try my best to answer them
