Once you receive the phone, you need to open the Shop Samsung app. There you'll have a message in your inbox (tap the menu button on the top left to open the options and go to that).
That will take you to a registration page and once you fill in your data (it will take the phone's IMEI and MAC automatically), it will be sent for validation. If all goes well, you'll get a confirmation e-mail within a couple days. If not, they might ask that you upload proof of purchase to confirm that you did pre-order the device.