Hello carben14 -
Unfortunately, you cannot add consignment associations to already active listings.
If you wish to associate items with consignors you have set up in your Auctiva account you would need to import the listings from the Closed Listings page of your account once they have ended on eBay into your Saved Listings in Auctiva and, after having set up your consignors and commission plans, edit the Saved Listings prior to re-posting them.
So, once you see the items in the Closed Listings you can use the 'Import Listings' button on the Closed Listings page to import such listings over to your Saved Listings. Then, in any particular Saved Listing you would need to use the checkbox for "Is this a consignment item?" and assign the consignor and commission plan to that item. You can then re-post the item from your Saved Listings.