What are you talking about?
Are you talking about an AAdvantage frequent flyer account? I can't think of any reason in the world one would need to formally "cancel" this.

Or are you talking about a Citi AAdvantage Mastercard credit card? Me thinks the latter, since I don't know how else you'd be "donating" anything from a frequent flyer account that you said you just opened and has no miles in it.

If you can't figure out how to cancel a credit card, I think you need a lot more help than we here can provide you.