Drill a small hole directly through the center of the bolt. Enlarge this hole by changing to a larger drill bit, continuing until you can insert the tip of your bolt extractor into the hole.
Tap the end of the bolt extractor lightly with a hammer to help the extractor's "teeth" sink into the material of the bolt.
Twist the entire extractor counterclockwise with a wrench or with an electric drill set to low speed. If the extractor is seated fully into the bolt, it should twist out.
Drill a small hole directly through the center of the bolt. Enlarge this hole by changing to a larger drill bit, continuing until you pick the remaining fragments of the bolt from the bolt.
Select a helicoil insert that is one size larger than the original bolt hole. For example, if the broken bolt is an 8 mm bolt, select a 10 mm insert.
Enlarge the bolt hole to the size of the selected insert by drilling it with the appropriately sized drill bit.
Insert the included tapping tool into the hole. Twist the tap 1/3-turn at a time, stopping once the tap feels like it is seated snugly against the hole. Then back the tap out slowly to cut new threads into the hole.
Insert the new insert with the included insertion tool. Once the insert is flush with the hole, punch out the installation tang on the insert with a metal punch.