Now that your dog has learned to speak on command, let’s teach him to be quiet on command. Tell your dog to speak or get him when he’s barking. Stand in front of him and tell him quiet, this is best when accompanied with a hand signal, such as your thumb and first two fingers together in a line movement across your chest (just like you are telling your kids to Zip it!). When he stops, even if its just between barks, give him a treat. Repeat until he does it on command. Keep training sessions short, about 5 minutes or so that both you and your dog do not get frustrated.
As your dog gets use to the quiet command, you can gradually increase the quiet time from 2 seconds to 5 seconds or more. Then, when he understands the trick, you can make a game of it. Tell him to “Speak,” “Speak,” “Speak,” and then “Quiet.” Then “Speak” again.