You can relist an item 3 ways  -

  1. If you still have one of it for sale find it in Selling  >   Items for Sale (or here), click on Edit Action and edit the Quantity field.

  2. If you sold one of these items go to Selling  >   Items Sold (or here), click on the Sell Similar  Action and make any changes if needed.

  3. Sell the item in the normal way (Selling from the Database, Selling from your Collection or Listing free form).