For a transaction to be connected to an affiliate, the buyer needs to click on the affiliate's hop link, on their website to go to your site to purchase the product, or the affiliate's direct link to purchase the product there.
The best route for this is to give the discount code to your potential buyers at the conference and include the URL where the affiliate's link is, so this way the buyer will be going through the steps necessary to connect the transaction to the affiliate. There is not a way to connect a discount to a specific affiliate.