How can i train my dog to not overreact to sounds?

the important thing here is not to accidentally praise him for doing this, dont comfort him and pat him while he barks and tell him its all ok! this will just reinforce the behaviour you dont want. tell him NO very firmly and grab him by the collar and make him sit, only pat him and tell him hes a good boy when he is being quiet. Practise this all the time not just when the baby is asleep, every time he barks say no, make him sit, themn lots of praise when hes doing what you want, which is being good and quiet.