You'll be sent an email as soon as you've been included for access for the first time.
You can register by following this link: https://app.onsi.com/welcome/freenow/gb
If Freenow by Lyft hasn't included you for access yet you won't be able to register. They update us each month with the details of the people they want to include for access so if you've recently started, this may prevent you from registering right away.
If you think you should have been included but haven't been you could consider reaching out to the team at Freenow by Lyft directly.