You need to get yourself a thread tapping tool of the correct size,,gring one of the bolts to your local parts store or rental store if you dont know the size and either rent, or buy a suitable thread tap.
once you've got the tap,,start the tap into the thread bore in question and be carefull getting it to start straight,,then take it slow and twist it in and out in 1/4 turns,,increasing at each turn,,until you are all the way in.
Then you should be good to go.