Look and figure out what size up bolt you would have to go to, so you have virgin metal for threads, then go to an autoparts , or hardware store, and buy that size tap, and it will tell you what size drill bit you need. Drill the hole out, be careful to stay as centered and straight as possible. Then using oil on the tap, pushing down hard, turn the tap in. I go about a turn and a half, then back it out a half turn, blow awayy metal shavings and give it another few drops of oil. Repeat until all the way through. Remove tap, and you have new threads, for the new proper sized bolt.