You can get a coupon for one free Double Jack, Jumbo Jack (with or without cheese), or the Habanero Ultimate Cheeseburger that they're apparently testing (if you happen to live in one of the test markets) by signing up on their website (you'll need to enter an email or phone number to get it).
The coupons are available until either 1 million have been given out or until the end of February 15, 2016, which ever comes first. You can expect to get your coupon within 48 hours of signing up and it's only available to U.S. residents of at least 18 years old.
As I mentioned in an earlier post, I had a feeling that they were going to run some sort of promotion for the new burger.
Here's the TV spot that ran during the Super Bowl revealing the giveaway: