At the gate, I have almost perfect success in getting a better seat when I fly confirmed. It’s all about understanding the timeline of gate agent seating changes.

First, continue to monitor the seat map regularly until you’re at the gate.

Once you’re at the gate, simply ask the gate agent about what time they’ll start clearing upgrades. Usually it’s D-40.

The nice thing is seat control isn’t usually taken until D-30, so you have a 10-minute window when the GA is moving C+ passengers to F while you can also move yourself. When upgrades start clearing, refresh the seat map continuously and try to poach a newly vacant and better seat.

You could also ask the GA to move you when better seats are free, but it’s unlikely depending on how busy the GA is.