Scooters have an engine specs sticker prominently displayed somewhere on the scooter body - usually on the tub under the seat.
There will be found the plug brand, type and gap.....as well as other engine specifications (like valve gap, idle rpm, etc.)
Surely your Kymco will have one of these labels?
I have it directly from emails with a couple* of company hq. that the sticker accompanying the scooter is THE correct source for all such info....regardless of the info in the owner's manual or any service manual.
Stig
*KymcoUSA, and Piaggio Hq in NYC. ("go with the sticker")