You can do it yourself, the good auto parts stores sell heli coil kits. You'll need metric 8x1.25 Kit, it comes with the drill bit, the tap and the coil install tool. Remove the head, bring the piston up to TDC nearest where you'll be drilling, cover everything so chips don't get in the engine. Measure depth of the hole you be drilling so you don't go too far. Transfer that depth to your drill with black tape. You can add a little grease to the bit to help catch chips but I wouldn't. Drill to near your measured depth keeping the bit square to the hole. Blow out the chips, use the tap to re-thread the hole, back the tap up slightly after every half turn to break the cutting chips. Be careful not to put any side load on the tap as they are brittle and can break. Slowly tap the hole to near bottom. Blow out, thread the new coil onto the coil install tool, you can add a small amount of red lock tight if you like to the outer coil threads. Don't use very much and right after install and for the next ten minuets blow out any extra lock tight that seeps into the inside threads. You can blot it with a que tip or paper towel. Lock tight not required, I almost never use it, works just fin without. Install the coil so it's slightly below the deck surface by like a 1 or 2 mm. The top coil end needs to be in a thread, don't want to catch the very top coil tip with the bolt and pull it up any. Use a fairly large punch to break out the ear at the bottom of the coil and remove it. Done re-Assemble
If you got some machanicle know how you can do it it's easy. You could practice first on a scrap piece of aluminum if you nervous first
Good luck
