Open a ticket with KI support, they're probably the best ones who can help. You can reach them by clicking the "Help?" icon in the upper right corner of this page.
Also, the test realm isn't actually up and running yet. (It might come out some time this week.) But if it's not running, that might be why you can't download it right now. So maybe wait a few days and then try again when the test realm servers are active.