I would like to participate in tomorrows open beta of WoW classic.
I’m unable to install.
I have done:
still, no option to install wow classic in the region / account drop down.
Am I missing something?
Were you invited to participate in the beta?
Hello Nequa 
Whether you’ve been added to the beta participant pool will be visible in Account Management, in the list of game accounts:
Battle.net Account - Games & Subscriptions
If you have not yet been randomly selected as a participant, you won’t see a WoW Classic or Stress Test account in that list.
Best of luck in your adventures 
To quote www.polygon.com
Everyone’s getting a chance to try World of Warcraft Classic during a stress test
World of Warcraft Classic is only in closed beta right now, but that’s about to change, at least for one day. On Monday, Blizzard announced that everyone in the Americas and Oceania with a current World of Warcraft subscription is going to get the chance to try out Classic on June 19.
The developer is temporarily opening the game up to every single WoW subscriber in order to give Classic ’s servers a serious stress test.
Client download for the Classic stress test will be opened later on today. best estimate I’ve seen is “late”
So I just got the option to start downloading the client for Classic stress test tomorrow. Everything stared out fine and the download very quickly got to 2 percent complete with 9.37 GB remaining. The client kept downloading for about another 10 minutes and the progress stayed still. After that the download just disappeared. Any ideas as to why that happened?