If your bad breath is coming from the crown in your mouth, then you are extremely lucky because all you need to do is to go to your dentist to have him clean it out and fix it. In fact, you need to do that as soon as possible before you get a very complicated and painful infection.
If your odor is not caused by a localized infection in your mouth, and instead coming from your lungs through your breath, then other factors may come into play here that are much more difficult to correct.
But if you think it's the crown in your mouth, then you should make an appointment with your dentist right away.