your auctiva store should automatically pick up your ebay listings. there is no way for you to tell it to update. you can, however, submit a support ticket and ask that they get it updated.
reason why you cant initiate the update yourself is because everytime the auctiva store does an update, ebay charges auctiva $. So, they have the store set to auto-update on a schedule. If it's been more than a few hours and items still have not shown up, then submit a support ticket.