Seats for Turkish Airlines through Air Canada

I recently booked three separate itineraries on Turkish Airlines all booked through Air Canada Aeroplan. One of the itineraries is mostly on Lufthansa and only has one short leg in economy on Turkish (MSP-FRA-IST-BJV). The other two are entirely on Turkish in business class (MIA-IST) and (BOS-IST). I have the Turkish Airlines specific booking locator but I have been unable to access the booking on Turkish Airlines' website or app and assign seats. Does anyone have any success with assigning seats when booking something similar? TIA!!