If you forgot to enter your Mileage Plan number when you booked your flight or don't get credit for miles flown, you can add miles before your trip by calling the Alaska Airlines reservations department at 800-252-7522. Or you can fill out the Alaska Airlines online mileage credit request form after you fly by simply entering your Mileage Plan number and ticket number. You must wait at least seven days after an Alaska flight to submit a request. Submissions must be within the last 12 months. Claiming miles for flying on a partner airline is allowed.