Before you can start repairing the damaged thread, you will need the following tools:
Make sure in advance that the single-cut tap and thread insert match and have the right size and same pitch.
In our example, the thread is free, so there is no broken screw. We describe how to remove such a broken screw in our article "How to remove a broken screw from a workpiece?".
How you even cut an internal thread is explained in our article "How to cut an internal thread in three steps".