The Orbi CBK752 is designed to replace an ISP cable modem. i.e. the device that connects to the coax cable coming from the ISP network into your house. It is not designed to connect to a fiber optic system.
https://www.netgear.com/images/datasheet/orbi/CBK752.pdf
The installation guide has instructions to connect the router directly to a cable TV outlet (or the coax cable if there is not an outlet).
https://www.downloads.netgear.com/files/GDC/CBK752/CBK752_QSG_EN.pdf
Notice that none of the pictures show a WAN (yellow) ethernet jack on the back of the router.
The installer did not do you any favors by placing the fiber ONT where it is not close to your preferred router location, and using the building coax wiring via MoCHA adapters to bring an ethernet link inside the house where it currently connects to their router. To replace their router, you need a WiFi system that connects via ethernet, not a coax connector. This Orbi will not work.
Sorry. You did not want to hear this.
