In the main menu:
click on the plane upper left.
click on Configure lower left.
click on Fuel and Payload
click on Manage Mass in EFB.
Now you see the screen where you can add passengers.
Or, also in the main menu:
click on EFB lower right
click on the aircraft icon.
click on Flight performances.
click on Mass and balance.
The EFB can of course also be accessed from within the aircraft.
All three methods work for me