The answer depends on the type of domain extension and for how long it has been expired.
For other domain extensions, it is possible to perform what is called “Domain Late Renew.” This means that the domain is out of the renewal period, but for an additional fee, it can be activated again. If your domain extension qualifies for “Late Renew”, the option will appear in the “My Domains” section.
If it doesn’t appear, please contact us immediately at firstname.lastname@example.org so we can check if something can still be done. If it is not possible to perform a “Late Renew”, and if you are still interested in the domain name, you will need to submit a new registration.