if the device has a single port, it's probably configured as a router anyway because that's what OpenWrt usually does so it has a static
IP 192.168.1.1, no gateway or dns server set up so it won't connect to the Internet (or even local network if it is not 192.168.1.x) in this state. Connect to Luci web interface at the mentioned
IP address and change the
LAN interface settings to add the
IP of your router as gateway and
DNS server. If you have only
SSH or console access, please see the
Use SSH to connect to the internet and install Luci Web interface article.