Exhaust system, thread broken down what to do?

Hello guys, after my car (which I bought only recently) finally from setting up and putting up chain again I thought to myself: The nuts on the exhaust mount (i.e. directly on the engine) were extremely rusty, so I got to work with rust releaser and gun. Well, and because after Fest, Ab arrives I unfortunately had not only the mother but also part of the thread in the hand (plug rusted in the mother). Does anyone have any idea how to fix something like this again. Can you??? Do you have to drill this or what does it look like?