Yam am ya Haas Nicolas

I think I have found the problem it needs to be re helicoid to the cylinder head does that sound right?

One of my spark plugs has worn away the thread were you screw it in would it be easier to get a new part were the spark plug goes or to get it re bored also what is the part called were the spark plug goes thank you for any help with this sorry for my novicenuss on this I don't know much about the mechanics of motorcycles what would be the price for getting it recoiled thanks