To get the early access you have to pre-purchase the game or the Diablo Prime Evil Collection. For the early access beta, you need to have separately pre-ordered diable 2 resurrected gold: Resurrected or Diablo Prime Evil Collection on each platform you want to play on, Blizzard added.

The open beta begins at 6pm UK time a week later, on 20th August.

The beta weekends for d2 resurrected gold: Resurrected, the remaster of Blizzard's 20 year-old action role-playing game, include two additional classes: the Druid and the Paladin. These join the three available to play with the previous alpha test: the Sorceress, the Barbarian and the Amazon. Diablo 2: Resurrected launches with seven playable classes.
Ariticle From:https://www.gm2p.com/diablo2-gold/