“Down” is a skill that can take some time to build. Like “sit,” it’s a good idea to teach the behavior with techniques called luring and shaping.
Grab a tasty treat and hold it up to your dog’s nose. This time, slowly lower the treat and push it slightly in towards your dog. It’s unlikely that your puppy will snap down on the first try. It may take a few training sessions! Instead, mark and reward any partial downward movement. As your dog continues to progress by dipping lower and lower, heighten your rate of reinforcement. Once your dog’s elbows hit the floor, throw a little party for your dog! Tell them that they completed the behavior by providing treats in a rapid succession.
Once your dog is regularly completing the “down,” add your verbal cue.
Like “sit,” if your dog is already familiar with this skill, take it on the go and practice in a variety of spaces and on different surfaces.