Hello,
Once you log in to your new device you should get an email with the verification code that you need to provide to the application.
If you don't get such email it means that you used the older version of the application before. When you first synced your vault we've sent you an email with subject "Your backup identity". In in you should find a "restore" link that you need to click and follow the instructions.
Please let me know whether I was able to help you.
Best regards,
David