Unfortunately, there isn't a lot that you can edit when you are trying to relist an item that is in the Closed folder (basically you can change the title, starting price, duration, etc.)
In order to be able to fully edit your listing, you can do that by going to the Saved listings and select which one you want to use. Or click on the "Create Similar listing" icon next to an item in the Saved folder and go from there.
If you are trying to re-list an item that didn't sell AND be eligible for a re-list credit on ebay, you would have to do so by posting the item from your Closed listings folder, re-post it to ebay, then go and edit your listing directly on eBay.