Found this old thread attempting doing the same. Since calling or messaging airlines is not practical due to coronavirus right now, tried various hacks to do it online. This is what worked for me: Alaska gives a lot more choices for check-in than for managing the trip. I attempted to check-in my reservation using ticket number from AA reservation, even though it was not time yet. As expected, it gave me the error explaining that it was too early, but it also gave me the details of the trip including Alaska record locator, which I then entered into "manage trip" field.