Login into the router interface by entering 192.168.1.1 into your internet browser. Then click on the Modem link which will then show a drop down list. Here you will click on the Connection Profile link and the page will show the APN line that you will fill in with your networks APN. No other entry is necessary on this page.
Once you click save the router will start to cycle and begin connection. You will need to wait a few minutes to initiate connection. You can view the status of the connection of the Network Status page which will start populating as the modem cycles and connect to the network.