When you jump in in public, you need to do three things. First, validate your boss. This can be simply, "Thanks for bringing that up, Kelly." That sends a signal to the room that your boss is smart and important. Next, correct, but not too overtly. Instead of saying, "That's the wrong number." Try, "We have some updated figures." Or, "It might be important to consider x." You want your intervention to be conversational, not directive. Guide your boss to the right place. Don't cut them off. Finally, flip the conversation back to your boss. After you've made the correction, you can give them back control by saying something like, "Thanks for letting me jump in here."