Through May 29 you can go to the promotion website, click “Don’t Have a Code” and enter your email address. Once you submit, the site will tell you whether you’ve won anything, and if so how many miles.
You can win up to 25,000 miles. But you might win nothing. You can keep trying using a unique email address (and refresh the promotion code) until you get a mileage offer you like, you don’t enter your mileage account number until the screen where they tell you if you’ve won and how many miles.
I admit, I got nothing my first three tries and gave up patience at 200 miles. But others have reported greater success, and it just takes a moment.