Very carefully drill out rivet after head is off it could be punched out with punch.
Be sure not to drill to far if you are sure whats on the other side of the A/C skin as many old timers will tell you stories of drilling in wiring, pipework etc.
True story coming up, a fitter drilled out rivet, made a mess of it, to cut a long story short ended up as a 6" by 6" insert repair.
The best advice is to be carefull when drilling it out.
