Welcome to the Community. You will need go to alienware.com. Select you laptop, and then click on customize, you should get 5 tabs on top, the second tab on top should say Personlize, click on Continue Personlizing should get you to the Personalized Plate. Refer to below link for more info.
If you have any other Alienware questions, post them on our Alienware Community page,. Our Alienware users or the Moderator of the site Chris Mixon, will be able to help you. Below is the link to the Alienware Community page.
Hope this helps.