In order to visit a detainee in Ellebæk, you must be approved for visiting. This is done by sending an application via email or regular mail to the Detention Center. The application form is available here
It usually takes up to 5 working days to process applications for visiting. If the application is approved, the detainee will be informed directly. You will not receive an answer yourself. It is also the detainee who will book the appointment through the guards.
You can read more about the time slots for visits and the application here (in Danish):