In any event, I've seen this attachment mechanism before. It's a long hollow thin walled tube that "clamps" the other end of the tip against the ceramic element.
the nut near the handle removes loosens.
When it's loosened, the tip won;t fall out. To replace the tip, you wait for the iron to cool and remove the nut at the end of the handle with the tip facing the ground. The tube will then contain a loose floppy tip. Turn the tube 180 degrees and the tip will fall out. From here, you can figure it out.