Go back to the article you provided the link to. On the right hand side of the page you will see a list of models the article applies to. I could not find the R6020. There is a good chance the option is not available on that model.
....router is on latest firmware, app is also latest version.
Not always a good idea. New firmware has been known to remove features, especially those that rely on Netgear's web services. They do that to make way for services that they can sell users. I doubt if they did this to the R6020. Too basic to be up to the new stuff. But I'd check the recent release notes for any warnings.
If you do get the R6020 to play ball, don't expect a lot. According to Netgear's manual for this device, not always the most reliable source of information, the LAN and WAN support only 10BASE-T or 100BASE-TX. That makes it slower than many newer Internet services and most modern network hardware. This may not matter to you, but be warned that it will hobble you if you ever sign up for faster Internet. It also slows down whatever is going on in your local network. Newer devices support 1000BASE-TX.
