To control Yeelight devices with this binding, you need to connect the device to your local network at first with the Yeelight app. This app is available in the iOS AppStore and on Google Play.
Then you need to activate LAN control mode by enable Developer Mode in device settings, after which it will become discoverable by openHAB.
Try changing the router config to use DCHP and set the IP range to whatever you like. That way all devices will be automagically assigned an address for your network.