Does the router contain a PlanetCNC-supplied controller (hardware)?
I suspect the router was sold with a counterfeit controller, and that is why the field is grayed-out. All legitimate (authentic) controllers have a unique license tied to the logic chip that prevents unauthorized coping and pirated use - to protect PlanetCNCs intellectual property.
Chinese suppliers sometimes try to cheat and work around these necessary barriers.
Your best option would be to tear out the counterfeit controller board and buy and replace with a legitimate, licensed, controller from www.Planet-CNC.com.