IT needs to be done at a dealer with a GDS machine.
Keyless entry remotes must be programmed by a Hyundai dealer.
If you can't find programming instructions you can get a programming guide from iKeyless.com
its a CR 2032
Must go to a dealer
You should have programming instruction in the user manual.
There should a programming guide in the users manual
There should a programming guide in the users manual
Cut and paste your question topic into Google. You'll get a hit for a Hyundai forum with lots of discussion about the keyless remotes, how much they cost, etc. Further down the page in earlier discussions, there are several explanations as to how to program them.
I found an Internet site which says how to program the keyless entry remote. But there is an error: this procedure is good for Elantra 2001 to 2003. Elantra 2004 must be programmed by the dealer. http://car.justanswer.com/hyundai/n1kw-program-remote-entry-hyundai-2004
I'd check the users manual for the programming guide.
You should have programming instruction in the user manual.
There should a programming guide in the users manual