Head over to callofduty.com/beta and follow the instructions on the page to reserve your spot in the Call of Duty: Black Ops 4 Private Beta.

You'll need to log in with a Call of Duty account and enter your Call of Duty: Black Ops 4 Private Beta code. If you don't have a Call of Duty account, you can create a free one. After creating your free account, you'll be sent an account verification email to the address you provided.