Hi,
If you're using RUTOS firmware - RUT2_R_00.07.01.X on your RUT240 then navigate to Network -> Interfaces and disable/delete WAN/WAN6 interfaces. Then edit LAN interface and in Physical settings section add eth1 to interfaces.
Once you'll save this configuration, your WAN port will start working as LAN.
If you're using old RUT240 WebUI then follow this guide.
