There’s an entry in Nintendo’s FAQ in regards to the Ambassador Program that refers to what is known as an Ambassador Certificate. Basically, this certificate “is a downloadable video available to Ambassadors.” The idea is that:
By tapping the receive button on the Touch Screen when viewing this video, Ambassadors will receive updates regarding the Ambassador Program, such as when new titles are available to download. As soon as details for the 10 Game Boy Advance Virtual Console titles are available, we will send an update to those who have opted in using the Ambassador Certificate.
So I guess if you boot up the Nintendo Video application it’ll be obvious enough what to do. Either way though, I’m expecting the information to find its way online soon enough.