Find it here:

Menu: Noise > Buildings > Number of persons

or

Menu: Noise > Buildings > Dialog box

Select one building in the list

Dialog box: Number of persons

Closes all dialog boxes before the following question:

Enter the number of persons in each building:

State a value and press <Enter> (or <Esc> to cancel the function). The value is now used as the number of persons for the selected buildings. This number is used in the reports on the number of persons within certain noise ranges.