Destiny 2 (PC) Beta starts officially on August 29 for everyone, but those who pre-order Destiny 2 (PC) get 1-day ahead of everyone else with an Early-Access codekey. For those who want a seamless experience at cancelling the pre-order you can get it here.
Within 2-3 days you will get an email from Amazon with the Beta Early-Access code. At that point:
1. To redeem the code, go to Bungie.net/en/User/Register (if you don’t have a Bungie account.)
2. Please choose a network to sign in with:
PlayStation Network, Xbox Live, or Blizzard (Choose Blizzard).
3. Login using your Blizzard Battle.net account credentials when the pop up window appears. It uses the Blizzard Oauth.
4. Go to https://www.bungie.net/en/User/coderedemption to redeem your code.
5. I am uncertain if they will give you another code. If they do give you another code, then it must be redeemed at https://us.battle.net/account/management/claim-code.html
If no code is provided at the Bungie Redeem Code page, then you are set already to download Destiny 2 (PC) on August 28 from your Blizzard Battle.net Launcher.
The second option (if you don’t plan to cancel the pre-order) is to pre-order directly from Blizzard here.
The Destiny 2 (PC) Early-Access Beta starts on August 28 via the Blizzard Battle.net Launcher. Everyone else gets access to beta on August 29. Beta ends on August 31. After that, Destiny 2 goes live for PC on October 24.