Login to Azure portal Virtual Networks > AzureNSvSonicWALL > Subnets.
Click Add subnet.
In the search box at the top of the portal, type the name of the VM to which you want to add the network interface, or browse for the VM by selecting all services, and then Virtual machines. After you've found the VM, select it. The VM must support the number of network interfaces you want to add.
Select Overview, under SETTINGS. Select Stop, and then wait until the Status of the VM changes to Stopped (deallocated).
Select Networking, under SETTINGS.
Select Attach network interface. From the list of network interfaces that aren't currently attached to another VM, select the one you'd like to attach
If you don't have an existing network interface, you must first create one. To do so, select Create network interface. To learn more about how to create a network interface, see Create a network interface.
Select Overview, under SETTINGS, and then Start to start the virtual machine.
NOTE: The newly added DMZ interface will reflect on SonicWall NSv.