You can go to your character’s page and in the upper-right is the current status.
Mouse-over on that, and click the link for Unretire.
In some situations, your character was retired or made inactive because you lost a scar match and never updated the design sheet. In that situation, update your character’s design sheet. Staff will be notified when your sheet has been changed, and carefully review your design sheet before reactivating your character.
If your new design sheet does not reflect your new scar, your request for reactivation will be declined.