That depends.
If your catalytic converter is just gunked up it is possible that fixing the problem that gunked it up in the first place may return it to effective use. But often they get chemically poisoned by things that should not go thru it like antifreeze, gasoline additives and motor oil. If this is the case then the converter must be replaced, there is no way to fix it on the car.
So a good first try will be to fix problems with the engine, maybe replace the oxygen sensors.
If your catalytic converter is just gunked up it is possible that fixing the problem that gunked it up in the first place may return it to effective use. But often they get chemically poisoned by things that should not go thru it like antifreeze, gasoline additives and motor oil. If this is the case then the converter must be replaced, there is no way to fix it on the car.
So a good first try will be to fix problems with the engine, maybe replace the oxygen sensors.