I have the same issue despite booking directly with TAP, on their website. However, I booked a stopover in LIS, and when I click on the link in the stopover email - and only the stopover email, not the booking confirmation email or by entering anything directly on the website - I can pull up my record and edit seats, FF number, etc. I discovered this after about 2 hours of trial and error, including different browsers, devices, the app, etc. Mentioning in in case it's helpful to anyone in the future - search your email for the separate email regarding your stopover and click on your booking from there.