If he tells us how, there will be a dozen people "repairing" chips in no time.

I'll make an offside guess that they take materials from other chips of the same color and powder that. Then they mold the new material into the hole and like magic, perfect repair. (I realize it takes a little more technique and effort)

Just like filling a cavity in a tooth.

Someone could make a nice H&C stamp in case it needed to be on that portion, and with some dental tools or jewlers tools, do the fine work.

I'm sure someone figured out how to restore the Hot Stamp long before anyone was repairing cracks and holes. Some might call it restoration. I really don't know what to think. But I can say, I'll never alter any of my chips, except cleaning them or removing junk that has been added to the surface, that isn't part of the original chip.