Call KE. They will assign the seat. IIRC, you can't get a seat more than thirty-something days before the flight, but as long as you are in the window and a G/P/DM it only takes a minute. You'll need the KE reservation number or your ticket number. I've flown that route at least a dozen times and never had a problem getting a middle aisle seat.

A couple other things... If you are in J, you will get a card allowing you to use the expedited immigration line. As a STE+, you are eligible to get the card, too. Sometimes they forget to give it to you in coach, so ask if you are in coach. But, sometimes the regular line is shorter than the expedited line. They are next to each other. If the expedited line is long, just go to the other line.

And going through ICN beats going through PVG for so many reasons, and the KE flight is much nicer than the MU or FM flights. The only exception to that would be if you want to tour Shanghai for a couple days while you are flying through. You can stay for up to 144 hours without a visa.