How can I arrange a technician to install the modem?

I received the modem from PostNL today, and I've tried several times to schedule an appointment for a technician, but I couldn't proceed because the details I entered from the contract are incorrect. What steps should I take to arrange for a technician to first install the phone cable and set up the modem? Additionally, do I need to make an appointment for a technician, or will KPN handle this automatically?

Best regards,