Setting up XR300 as Extender

Hello,

XR300 1.0.3.56

I'm trying to see if its possible to set up my old XR300 as a Wifi extender for my current XR500 without being wired in. I want to put the router in another area of the house that is getting a really weak signal. I've followed the steps here but when following the prompts on the Netduma interface, I only see Access Point. I've followed those directions and it seems the image wants the XR300 plugged into the XR500, which it does give a Wifi Signal from the XR300, but I'm wondering how it could extend without being wired in.

Thanks!