I booked a UA ticket on Expedia. When I booked the ticket, Expedia did not have my FF number so it was not added to my reservation.

I went into my United app and added the reservation to my the app on my phone using the confirmation number. I clicked on "accruals of this trip" and it said if I was a MP member I should add my FF number to see my accruals for this trip. But there was nowhere to add my FF number there or anywhere on to the app. Am I missing something? It seems like if a third party makes a reservation for you without your FF number, there should be a way to add it to the reservation once you pull up the reservation on the app.