Apologies if there is a more obvious thread to ask this, but Monday morning

Flying out to ORD in April. Over the last few weeks the flight has been switched seemingly from a 777 to a 710.

We had paid for exit row seats in economy, but the seat plan obviously does not match up. It still has us in 26k & J but those seats don't exist in the Economy. The website is saying we can change to any free seat, which everyone is, but it won't let me actually click on anything.

What is the best way to go about sorting this?

Thanks!