If you are looking to relist items that did not sell in an earlier event, you can do so by navigating in your Members Area > Selling > Closed/Sold section, click the "Filter by" drop-down button and select the "Not Sold" option:
This will show you all of your closed listings that never sold -- auctions and store items.
You also have the option to use other filters to further narrow down your search on the right portion of your Closed/Sold page like the Start and End time, as well as the "Show Only" filters:
If you want to relist all listings that did not sell that ended on a certain date, these filters will show you the listings you're looking for in just a few clicks.
Then, to relist them, at the top left of the page, click on the drop-down menu connect to the first checkbox, and then select the "Select All ## Matching Listings" option:
Then scroll to the bottom of the page and click on the "Relist" button. A small window will then appear where you can select whether to relist the selected listings as store items or put them up for auction.