To do it properly the head would have to come out...The rest of this advice is do at your own risk...They have spark plug thread repair kit's (you can google them) the problem is you risk getting debris, metal shavings into the combustion chamber...

I don't know how bad you stripped it, but i'd try vacuuming the plug hole out and using a fresh plug with some oil on the threads and try to put it in, it's worth a shot...

 

The kits work but you have to make SURE both valves are closed.

Steve

 

Thanks for the advise. I tried but seems I did it worse now. Damn. Seems that I needed to take the top stuff out to reach the head cuz doing it like that not enough room. I realize too late. Thinking I didn't needed room to thread it correct. Which I did.