If your device has some ports labeled LAN and at least a port labeled WAN and you want it to operate as a router (a connection between two different networks). Depending on actual hardware support, it may be possible to create a WAN port on a device with only LAN ports, see your device's page for more info about this.
the default IP of the LAN ports of a OpenWrt device is 192.168.1.1, if the addresses of the devices in the network you connect to the WAN port are 192.168.1.X (X=any number), you need to change the IP address of the LAN interfaces your OpenWrt router to 192.168.2.1 (or to something that isn't 192.168.1.X, anyway), or change the addressing of the other network you are connecting to.
The LAN and WAN ports MUST have at least different subnets for routing to work.
Command line instructions:
uci set network.lan.ipaddr='new-ip-address' (“new-ip-address” is the new IP address you want for the LEDE device in your network) and press Return,
uci set network.wan.proto='static' to switch to static protocol on WAN interface, then change wan settings by using the same procedure detailed for Client device, settings for wan interface are
network.wan.dns, and so on, so change the commands accordingly.
uci commit && service network restartand press Return