Hi Benjamin,
to enable "Access Control" / "Zugriffssteuerung" You have to change life cycle type from "basic" to "advanced".
To do that, deselect the current life cycle phase by clicking on the white area besides the different phases (e.g. click on "Klicken Sie hier, um die Eigenschaften des Lebenszyklus anzuzeigen").
After activating "advanced" mode, you are good to modify everything you need.
Cheers
Matthias