If it’s running Mackie mode then hold down shift and press the Master button, or Shift+Plugins and you will go into quick controls.
Press the Flip button to move the quick controls between Faders and V Pots (Rotary knobs).
Have you got a Cubase overlay for your B+ so you know which buttons they are?
One other thing, does the Platform B+ show as a second device in Cubase (In addition to the M+)? If it’s separate then that can be a big problem as Cubase will try to spread controls across both units if they are set as MCU’s which will be very confusing if you’re wanting to control anything over 8 faders/vpots.