If you had purchased the CBT access on the store.gaijin.net, then the key for the Steam version was sent to the email box of the account you had purchased the access to. If you still have not received the email with the key, please contact our Support: How to submit a support request
Please note that the key to the game is sent only to the accounts of the players who purchased the CBT access. The key to the game is not sent to the accounts of the players who received the CBT access by applying on the official game site.