Wait, the Dealer stripped the threads while they were doing work for you? Work that you paid them for?
If that's the case, it's their screw-up and they need to fix it for you (and fix it for free) , not give you the brush off! Go back and be polite, but firm. If the counter guy is not being responsive, ask to see the owner. Make it clear that they need to make the situation right.
To answer your original question. The carb float bowel screw threads into the carb body. The threads are small, metric M4 I think. I'm assuming that it's the threads in the carb body that are damaged, not the screw? To make new threads for a hole that small you have to drill a slightly larger hole and use a metric tap to cut a new set of slightly larger threads (M5 or M6). If you've never done that before, this is not a good place to practice so I'd advise taking it to a reputable dealer and having them do it.
Still, I think you need to go back to the dealer that did the jetting change and have them make it right.