I found this under the Saved Travelers section of the web portal. I corrected the birthday here. Does anyone know if that corrects it for previously purchased tickets?

If you book travel for others, add them to your account to save time during the booking process. Providing information to us means you have obtained permission from the traveler to do so.

To comply with the TSA Secure Flight program, the name, date of birth and gender on your MileagePlus account and flight reservations must exactly match your government-issued ID.