I think there are a couple of youtube videos that show this not sure if they are any good.
This is what happens when you buy a router not targeted at end consumers, you have to learn much more. What "gamers" and your home users call dmz is far different than what someone who want DMZ in business install.
The concept of DMZ is similar to the military version. There is a wall on both sides of the DMZ with restrictions about what can get in and what can get out. It is a separate area between the outside router and your lan. It is one of the safest ways to have a server exposed to the internet.
The consumer version is actually one of the most unsafe things you can set on your router. They only used the term DMZ but it is...