Go to the menu and it's under settings or one of the tabs in the bottom right. You will see a redeem button. Be careful though, there is a bug related to this:

https://www.vg247.com/2016/08/11/no-mans-sky-pre-order-bonus-ship-is-causing-a-game-breaking-bug/

I've seen they play this game on twitch, with the alert about the DLC ship popping up all the time .. can I choose to not download the DLC content so I won't get this message? (I'm still waiting for new pc to arrive so I can play it ^^P)

The pre-order bonus was late. I had already downloaded and was playing the game when it dawned on me I had not recieved the pre-order bonus. I went back to GOG and there it was. It wasn`t there when I had previously downloaded the main game.

To be honest I was glad i hadn`t recieved it too soon. the best part of the game is struggling to get started.

Yeah I'm enjoying the struggling to get started part. I'll wait until I've learned how to build a hyperdrive before I claim my pre-order ship. Just in case.