The COU Selector will present a simple dropdown of available COUs, optionally filtered by Configuration Label. When selected, the Petition cou_id will be populated, then during Finalization any Person Role created by previous steps will be assigned the specified COU.

Optionally (for invitation style flows) the list can be filtered to the COUs the Actor is an Administrator for (CO or COU) or a member of. This would most likely be set via a plugin configuration.