I usually check in at the airport watching the seat map from my phone until I'm happy with what's available. I've managed to get the 'stretch' seats a few times. One time it back fired with our party of 4. Rows 1-8 were all that were left on the 321, 3 of us got row 8 but at some point in the 30 seconds from looking at my phone and doing self check-in 41D opened up and my 4 year old was assigned it. I had no issue fixing it at the counter.

Can anyone advise as to how to pre-select a seat preference? I don't see an option whereby one can insert a general seat preference.