You can't create an account here. You should've received an account activation email with a link that will allow you to create a new account.
If you haven't received that email, please check your spam folder: it often ends up there. The email has a subject "Activate your Relevanssi Premium support license" and it's from mikko@relevanssi.com.
If you can't find the account activation email, please send an email to mikko@relevanssi.com. We also automatically resend you the email if we notice you haven't created an account yet.
Thanks!