When you want to Claim Avios and Tier Points for Alaska Airlines you have To do the fowllowing:

1.Choose other Airline
2.Choose ..want to Claim Avios and Tier points from a one world Partner Airline.
3.A Form popps Up,fill Out the Details of your booking,Like Flightnumbers, departure Date , Location of departure and arrival.
4. attach your booking and your Boarding passes.
Upload Form and Attachments,BA will do Tier points and Avios in one day(that was the Case at my inquiery).