REF: https://www.netgear.com/support/product/LB1120.aspx#ConfigurationAssistance_CommonTopics

To add a custom APN profile manually, use the information that correlates with your plan type. See below

-Blue Plans- APN: broadband
-Pink Plans - APN: b2b.static
-*Red Premier Plan- APN: vzwinternet

To view APN profiles or add a custom APN profile for a specific carrier network: 

1. Launch a web browser from a device that is connected to the modem. The device can be a computer that is directly connected to the modem or a client from a router that is connected to the modem. You can also download the Netgear Mobile app to make APN changes by logging into the modem thru the app.
2. In the address field of your preferred web browser, enter: http://192.168.5.1. The limited Dashboard page displays.
3. If you did not select the Remember me check box when you logged in previously, enter the modem password in the Sign In field. See the modem label for the default password. - If the default password (case sensitive) on the label doesn't work, conduct a factory reset on the device by pressing in the reset button on the backside (small hole) for 40 seconds
4. Click the Sign In button. The full Dashboard page displays.
5. Select Settings > Mobile > APN. The APN page displays.
6. To see details about the active APN profile, click the Details button. If you did not yet add a custom APN profile, the default profile is the active APN profile.

Manage the Mobile Broadband Connection Modem LB1120 and LB1121
 

7. To add a custom APN profile, click the Add button.
8. Enter the settings for the new APN profile as described in the following table.

-Name: name or acronym of the mobile broadband service provider or any other information that might help you to identify the APN profile (name it ATT OR T-mobile.)
-APN: "broadband" (AT&T) OR "b2b.static" (T-mobile)
-Authentication: click on the dropdown and select "none"
-PDP: click on the dropdown and select: IPV4
-PDP Roaming: click on the dropdown and select None


9. Click the Save button. The new APN profile displays on the page but is not the active profile until you select it as such.

Select an APN Profile to use for connection to the carrier network (You must select the APN profile you just created) 

The modem uses the selected APN profile to establish a connection with the mobile broadband network of the service provider. To select an APN profile as the active profile:

1. Launch a web browser from a device that is connected to the modem. The device can be a computer that is directly connected to the modem or a client from a router that is connected to the modem.
2. In the address field of your browser, enter http://192.168.5.1. The limited Dashboard page displays.
3. If you did not select the Remember me check box when you logged in previously, enter the modem password in the Sign In field. See the modem label for the default password.
4. Click the Sign In button. The full Dashboard page displays.
5. Select Settings > Mobile > APN. (The APN page displays the available APN profiles. If you did not yet add a custom APN profile, the default profile is the active APN profile and you cannot select another profile until you add a custom profile)
6. To see details about the active APN profile, click the Details button. If you did not yet add a custom APN profile, the default profile is the active APN profile.
7. Select the radio button next to the APN profile that must become the active profile. The APN profile is selected. The modem uses the selected APN profile to establish a connection with the mobile broadband network of the service provider

REF: https://kb.netgear.com/31166/How-to-configure-APN-settings-for-4G-LTE-Modems