Step 1: Open the web browser and type the IP address of the router in the address bar (default is 192.168.1.1) and press Enter.

Step 2: Click on the plus sign next to Objects and select Address Book.

Step 3: Click Add and select Address Folder from the dropdown menu.

Step 4: Enter a name as desired (route_addresses in this example) and click OK.

Step 5: Click Add and select IP Address from the dropdown menu.

Step 6: Configure the IP Address as followed:
Name: Name as desired (remote_local in this example)
IP Address: Local address to the connected device (192.168.1.20 in this example)

Click on OK.

Step 7: Configure the IP Address as followed:
Name: Name as desired (remote_gateway in this example)
IP Address: The devices LAN address (192.168.70.1 in this example)

Click on OK.

Step 8: Configure the IP Address as followed:
Name: Name as desired (remote_network in this example)
IP Address: The network identifier of the route (192.168.70.0/24 in this example)

Click on OK.

Step 9: Click on the plus sign next to Routing and select Main Routing Table.

Step 10: Click on Add and select Route from the dropdown menu. Configure the route as followed:
Interface: lan
Network: remote_network (from step 8)
Gateway: remote_gateway (from step 7, may not be required based on the route)
Local IP Address: remote_local (from step 6, may not be required based on the route)
Metric: Set to the desired value

Step 11: Click on the Proxy ARP tab. Select the desired interfaces to publish the route, or select Always select ALL interfaces, including new ones. Click on OK.

Step 12: Click on the Configuration tab and select Save and Activate from the dropdown menu. Click on OK to save and activate your changes.