Here is what EA says you need to do to get access.
If you are an Origin Access or EA Access subscriber or if you digitally pre-ordered on Origin, Xbox Store, or PlayStation Store, you have been automatically registered for the VIP Demo & do not need a code.
If you've pre-ordered Anthem through any other retailers, you will need a code to access the VIP Demo. Please contact the retailer you pre-ordered from to obtain your code.If you are an EA Access or Origin Access Subscriber, or Pre-Ordered the game, you need to Sign In to access the Friend Pass page.
Sign up here if you have not per-ordered.