when I try to add a full set or illustration rare card to my deck, it just turns into the normal card and will not display?
Click on the regular art and then the "Available" drop-down below the card.
Tap/click the “available” tab when selecting a card, it’ll show you all versions of the card and which ones are available to you.
Also, please use the forums’ search function to see if anyone else has asked the same question you have. There’s a good chance it has and the answer you're looking for could be in those threads.