XB, I suspect you'll be hard-pressed to find a good resolution in that area. If it were further up the wall, you might squeeze more time out of the pool by cutting-out the rusted area and applying a new piece of sheet metal from the inside as long as it can still support the opening, then also apply an anti-rust inhibitive spray. But at the bottom seam it would be very difficult. You can try to manipulate a metal patch, but I suspect the support ring is also corroded, and at some point the structral integrity comes into play. If it were me, I'd begin preparing for a replacement, however I'm also going to ping one of our AGP expters
@zea3 who has quite a bit of AGP experience herself. I wish you luck. And welcome to TFP!