[TYPO3-project-seminars] multiple seats: Where can I enable the excludefield "attendances: number of seats"

[Kerstin Finke]

Hi,
I want to setup the "multiple seats" feature.
In the documentation I found "enable the excludefield Attendances: 
number of seats" and I should add "Names of the attendees".

The problem: I can't find this excludefield. Where should it be, in the 
configuration for "seminars" in the extension-manager? Or should I write 
in the template / setup ??

Thanks in advance
Kerstin