X3000 connect lan port to guest network?

As the title says, is there something in the settings that will change the lan port from the private network to the guest network? I want to extend the guest network to another router in ap mode via a cat5 cable. I don’t want to use Wi-Fi extender mode because the second router is inside a steel building and the signal is weak.

I was able to do this by basically following the instructions here. Those instructions are for a different device, but same idea. Instead of eth3, move eth1 from br-lan to br-guest. Worked perfectly.