Double NAT - Need to Put HG8145V5 into Bridge Mode

Hi, there.

I have an instance of double NAT that needs to be resolved.  I am using a mesh network in my house with the HG8145V5 as my fiber modem/wireless router.  For me to solve this issue, I need to put the HG8145V5 into "bridge" mode (or so I have been told) and then do the port forwarding through the Velop interface.  I have looked in the menus for the router but cannot find a menu drop down that says "bridge" mode.  How do I get this resolved?  I can put the Velop into Bridge mode but that is problematic with the way we have our NASs and Printers shared.

Edit: found it but it is unable to be changed - I click on the "Wan Mode" dropdown but it doesn't do anything - the ISP has it locked.  I also have a "triple" NAT situation.  Below is what I am talking about:

ISP 10.x.x.x/30 IP

Incoming to ISP router - 10.x.x.x/30

Outgoing from Router to LAN - 192.168.100.x/30 IP

Incoming from LAN - 192.168.100.x/30 IP

Home LAN - 192.168.1.x/24

So all IPs assigned to the network here are private IP addresses and not public.  I need to have a "public" IP from the ISP to be able to access my Plex server on the NAS from outside the house.  :(  I guess I am hosed - I do not speak Spanish and my ISP is in Mexico.

Thanks.