Seating

i have booked a flight from Nanjing,china to seoul and then to seattle,usa.however when i did the online booking to choose my seats it did not give me or have the option of choosing my seat.what concerns me the most is the long flight from seoul to seattle and i would desperstely love to have an EXIT WINDOW SEAT as i have very bad knees and lower back and if i am unable to stretch my legs out my back will give me tremendous pain and my knees will swell up.my reservation id is 2LX4VR---booking number--11339005---confirmation----CKX5VQ--E TICKET---9887100577735.THANK YOU SO MUCH.I have tried to telephone the airlines from China but it doesnt work.my phone number here in china is 13515251632.