The LTE3316 can use it's first LAN-port as a WAN over Ethernet port. To use this WAN fail over you have to log on on your router using by default 192.168.1.1 User: admin and password: 1234
In the blue band-menu click on Configuration and navigate to Network > WAN > WAN Management. Choose WAN-2 > Action > edit
Tick "Port 1 config as WAN port", choose if you have a Dynamic IP, Static IP or a PPPoE connection. If necessary enter the needed informations in the fields below and click on Apply.
Congratulations. You have successfully set up the WAN fail over on your LTE3316