[Big hammer]

Remove the head of the rivet by grinding, or by drilling with a larger bit than the rivet shank. The rivet shank will then need to be driven out. If it not move easily then you will need to carefully drill it out, Don’t enlarge the base metal hole or you will need a larger diameter replacement rivet. Take you time don’t get in a hurry. Back up the base metal if you try to knock the rivet shank out with a Big Hammer!