Reattaurueth17 Welcome to the community!
The Connect app is designed to control one modem. As your account shows three modems, you will only be able to control the Fibre modem. As far as I know, there is no solution to this yet, unless you assign each modem to a separate customer number, in which case you can control them using their respective customer numbers.
Personally, though, I would keep everything together, as separating them would also mean 3 bills, 3 My Sunrise logins, etc.
Greetings
Daniele