You can now preregister to play Diablo Immortal via the Battle.net Launcher. Upon login you will see a splash screen like the below.
Then you can click through that to the registration screen, or you can go directly to the Diablo Immortal section of the launcher via the picker. Battle.net Launcher Direct Link Check out our other coverage of the announcement via the links below, as well.
Read more on wowhead.com