This wont be some super in depth tutorial, it's super simple.
Just pre-order the game on amazon, (you can use real/fake payment info, though at your own discretion). A code will be promptly emailed to you (email used for amazon account). Then, if you don't wish to buy the game just cancel the preorder in your amazon orders, or you can just leave it if its a new account with incorrect details on it.
*You wont be charged until just before release so dont worry if you use your payment info*

Pretty sure this is the same for most pre-order stuff on amazon. Just posting this so you dont have to sit begging for someone's giveaway who's probably just doing this to get codes, and so you dont buy a beta code as I've seen a few being sold.