Accessing Orbi Login.com through a fios g1100 gateway

Orbi can be managed two ways:

• Using the Orbi "app", which is slick but cannot be used to set up anything beyond the most basic functions.
  The app uses the Netgear forum login and password.
• The Orbi web interface, which has access to all settings.
  When the Orbi comes "out of the box", the login consists of a user ID "admin" (which cannot be changed)
  and a password "password", which the user is encouraged to change.
  If an incorrect password is entered three times, the Orbi pops up a "Password Recovery" web page where the user can enter the product serial number and answer some questions.

So, if the admin password has never been changed, it should still be "password".

Since you want to put the Orbi into Access Point (AP) mode, the only "settings" that matter are the WiFi name and password, so there is not much problem in performing a Factory Reset https://www.youtube.com/watch?v=cMw4ePACgc4 which will restore the web interface to "admin" and "password".