How do you rename your dog in Nintendogs in 3DS?

First, after you buy your dog, play with it a little. It doesn't matter which toy you use, as long as it doesn't bother the dog (items like the Mario Kart). Make sure you have a name chosen for your dog. I find it helpful to choose a name while you play with it. Sooner or later, your screen will go white (for only about 2 seconds) and then your dog alone will appear. After that, follow the instructions and call the name of your puppy into the mic (microphone).