If an alloy pop type rivet, use a knife tip, twisting it back and forth. You will see the alloy peeling off. Sooner or late, and likely sooner, the rivet will free up and you can gently remove the headbadge. Or...

If not a pop rivet style, I remove the fork and push the rivet out from the inside of the steering tube. You will have to figure out which tool(s) to use to achieve this. For me, it is a long screwdriver, a sturdy one, and a bit of leverage. You might even offer a side tap or two to the rivet end that is sticking out of the inside of the head tube...





For installation, get a proper pop rivet and rivet installer. For the other kind, get a screw rivet and tap it into place. I am lucky enough to have a dozen, or so, of those rivets and even the correct drill bit size to make the rivets fit properly.