You can find the DMZ Setting at http://192.168.1.1/ by logging in with the username of admin, password being the router's serial number found on the bottom front sticker of the router. Click Firewall settings, and from there on the left hand side navigation you'll find the DMZ option.
I do advise using the DMZ on a temporary basis, since it forwards everything to your security system. You'll want to use it for troubleshooting purposes only.