To add a route, you can use the following command and replacing <destination>, <gateway>, <interface>:

Once you have confirmed the route is working, you will need to add it to configuration file to make sure the route survives a reboot. Replace <interface> with the interface name
Once you are in the file, add the route like you did above without the commands:
You could instead, add the route straight into the configuration file and then run the following command to test the file: