Thanks for posting your question here.
If you associated an item with one of your consignors when posting it through Auctiva and you do not recall which consignor the item was sold for, I believe the easiest way to confirm that would be to look up the item on your Saved Listings page and check which consignor you selected in the "Is this a consignment item?" area under the description editor.
We do not currently offer any functionality that would allow you to associated a listing with a consignor you have saved within Auctiva after the item has been listed so it will not be possible to use our consignment functionality for items you posted before signing up with Auctiva.
I will share your comments in this regard with our Product Management team as a suggestion for future consideration though.
I hope this helps!