In addition to simply waiting for the lockout period to expire, Workspace or Subscription Administrators can manually unlock user accounts by going to Setup > Users and clicking the Edit option for that individual.
When a user is locked there will be a checkbox with the label "This account is locked. Click to unlock". Simply uncheck the box, select Save & Close and the user will beable to try accessing CA Agile Central again.
It may also be helpful to select the box for "Did this user forget their password" at the same time so the automatic password reset email will be generated and the user can update their credentials.