I just had the same problem where I forgot to provide my TSA pre number (aka Known Traveler Number) at the time of booking the ticket. Two hours before the flight, after online checkin, I realized my mistake. But I was able to pull up my reservation in the app and update the KTN there. And then retrieve the boarding pass again. This time the boarding pass has “TSA pre” printed on it.
In the app, when looking at the reservation, click on “Details” and then on the little edit button next to the passenger name. Then scroll down to KTN and type your number there. Wait a few minutes and retrieve your boarding pass again. That’s it.
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