You can easily restore any events you have archived if you need to use them again.
To restore an event, navigate to your Administration panel, and under Live Sessions/In-Class Training select Manage Events.
On this page, filter for Archived Events, so you may find the event in question.
Once you find the event in question, click on the Manage Event option, and then select Restore. Then verify in the box that appears.
Your event will be restored as Active.