1. Navigate to Interfaces | OPT1.
2. Check the Enable Interface checkbox:

3. Set Description to DMZ.
4. Set IPv4 Configuration Type to Static IPv4.
5. Enter an IPv4 Address and the CIDR. In our case, we will use 192.168.2.1 and select 24 from the CIDR dropdown list.
6. Leave IPv4 Upstream gateway set to None.
7. Leave the Block private networks and Block bogon networks checkboxes unchecked (they should be unchecked by default).
8. When you are done making changes, click on the Save button. When the page reloads, click on the Apply Changes button.