If the catalytic converter is only partially clogged then you can clean the clogged catalytic converter using some catalytic converter cleaner that you add to your gasoline.
You dump the bottle of catalytic converter into your gas tank after every fill up or before every few fill ups and then after a few tank fulls of gasoline with the catalytic converter the catalytic converter should be cleaned out.
However if the catalytic converter is more severely clogged then you'll need to have the catalytic converter cut off and a new catalytic converter put in it's place.
Also catalytic converters do eventually go bad and need replaced and a bad catalytic converter can cause your check engine light to come on and your vehicle can fail emissions testing.
So if your state or country requires emissions testing you may need to have your catalytic converter replaced if the check engine light is on and the catalytic converter cleaner doesn't clean it enough.
Other things such as bad spark plugs, bad ignition coils, loose gas cap, clogged fuel injectors or clogged fuel injector etc can cause a check engine light to come on as well.