Hello, friend.
1. Click Advanced Configuration > Forward Rules tab, and choose DMZ Function in the navigation tree on the left. In the pane on the right, click New. In the dialog box that is displayed, set the parameters related to the DMZ, as shown in the following figure:

2. Click Apply.
The demilitarized zone (DMZ) is a technology that enables the ONT to forward all received packets through a specified internal server. The technology enables a computer in the LAN to be completely exposed to all users on the Internet or enables the mutual communication without restrictions between a host with a specified IP address and other users or other servers on the Internet. In this way, many applications can run on the host with the specified IP address. The host with the specified IP address receives all connections and files that can be identified.
NOTE: If the LAN-side device does not provide website service or other network services, do not set the device to a DMZ host because all ports of a DMZ host are opened to the Internet.
Parameters related to the DMZ

Thanks.