GL.iNet GL-X3000; different networks on LAN/WLAN


I would like to have different subnets on LAN / WLAN. WLAN should have DHCP for usage as a mobile router.
Additionally the device should be used as a backup gateway for my home network and therefore the ethernet port should have a fixed IP, that is different from the subnet used for WLAN. DHCP needs to be disabled on this port.
How can I do this? If needed, I can do console configuration as well.
Thanks in advance!