Once you are logged into the DiamondBistro, if you click on the "my active listings" button, then from there you should see a menu bar featuring the options of Title, Current Bid, Sold? and Statistics.
Click on the white square in line with the item you have sold, under the Sold? column. This will toggle the icon to display beside the item title.
Note that as these are classifieds type listings, and not auctions, items are not automatically marked as sold and this must be done manually by the seller.
If you are already logged in, this link should take you directly to your items for sale: https://diamondbistro.com/index.php?a=4&b=1