You can specify the set by selecting it in the interactive deckbuilder or writing [EMA] in front of the card name in the text-based one. However, we unfortunately do not have card images available for all sets, and it looks like right now the EMA
counterspell is one of the missing ones. So while the set will be shown in your deck table and the correct image might be shown in the future, at the moment you will still see a different one.
Update: Actually, I just added EMA card images to our database. So if you clear your cache, EMA card images should be displayed properly now!