Joe Ks suggestions are good, and I’d try them first. But the bubbles are pretty large and numerous. I’d try an easy fix on a couple bubbles, and if no success, I’d carefully pull the covering off the panel and re-stretch the covering over a new panel and start over. It’ll be tough to find a covered panel that’ll match your other panels and seats, and it looks like the panel is simply a cardboard panel covered with the same vinyl as the seat. So peeling the vinyl off without stretching the vinyl too much, and gluing to a new panel (or the old one properly prepped for smoothness) would work.