@Daverie 

The ISP usually supplies a router that is able to pull the internet from the fiber optic cable which the Deco can not do. What you will likely need to do is wire the Deco into the Fios router.

You would also want to disable the Wi-Fi on the Fios and only utilize the Deco network.

If you want to keep the Wi-Fi on the Fios, make the name of the Deco different. Having the same name will cause connection drops as one device goes from the Deco to the Fios.