Just called in to try to select seats via call centre, no dice. Roundtrip YVR -> BUS via IST -- all segments on TK

1. You need the Turkish six character PNR. I found it by logging into the booking on AirCanada website and clicking on the booking, it's in small text under the AC booking code
2. The TK app works for accessing your booking, TK website won't allow it since booked via outside channel
   1. What you can do in the app:
      1. Request special service request/mobility assistance
      2. Select special meal
         1. Asian vegetarian
         2. Child
         3. Diabetic
         4. Gluten-free
         5. Kosher
         6. Strict vegan
         7. Jain/Hindu Vegetarian
3. TK Call Centre will let you select seats, but there is a charge $~39USD/51CAD (YVR -> IST -> BUS)
   1. see more details 3/4 way down page: turkishairlines.com/en-ca/flights/fly-different/seat-selection/
4. When checking in online, you will be automatically be assigned a seat (not able to select)
   1. If you check in within 6 hours of the flight, you will be able to select your seat for free