I don't see a feature where I can change the operational mode from open to Hybrid or closed on the Web Admin page
That option has been broken on the web site for several years. If you search this Forum you'll find numerous threads discussing the issue.
Is your extender stuck in Hybrid mode? I heard of someone's extender doing that which messed something up. Tech support would be the only folks able to fix that situation. But otherwise as jav6 said, the closed mode thing hasn't worked for quite some time. If your neighbors or other people are randomly accessing your service, the only thing you can do is lower the range of the extender. I have instructions elsewhere which another forum member had provided on how to do this, if you're interested.
To access the Managed Access (CSG) feature for the ASK-SFE116 LTE Network Extender, it will need to be registered to your Verizon wireless account and 'In Service' where you will manage it via the My Verizon Website rather than the extender’s embedded admin web server GUI.
The feature is partially working now as Verizon’s engineers continue to fix the flow completely through newer builds.
Note: Any changes you make below will cause the extender to temporarily lose its connection after receiving a call to restart and reboot with the configuration change pushed. Wait for the extender to come back online with ‘In Service’ on the display screen before testing with your mobile device cellular connection set to LTE only. If the steps below don't work for you especially the closed mode, the only alternative left to try to help mitigate is by the Transmit Power method as indicated by the poster above.
My Verizon Wireless users:
My Business Wireless users: