1) Log into your Fios router and find the Fios devices on your network (cable boxes, etc.) and record their IP addresses that are provided by the Fios router. Let’s say that you have a couple boxes with addresses like 192.168.1.220 and 192.168.1.226.
2) Restrict the range of IP addresses that are provided by the Fios router to encompass these devices. Let’s say you keep DHCP active, but limit the range to go from 192.168.1.200-255.
3) Then permanently assign the existing IP addresses to the Fios devices by giving them static addresses in the Fios router.
4) Finally, put the Orbi into router mode, and similarly restrict its DHCP range from 192.168.1.1-199.
Now the Fios router is happy serving its devices, and the Orbi can serve everything else, and Circle can interface with Orbi.