this will explain it for you re; helicoil an tapping.
as for what to do go to a local machine shop either with the bolt itself an get the matching helicoil kit to fix it yourself or
if possible remove the motor strip it down an take it to the machine shop with
all the bolts (head bolts) an they can do it for you it shouldn't cost much at all
reason i said take all the head bolts is so they can clean them all up for you (threads)
while doing the helicoil.
personally i'd get the machine shop to do it for you unless you are experienced with doing this kind of stuff.