Instructions
Load "Pokemon HeartGold" to the main menu. Tap "Connect to Pokewalker" on the bottom screen of your Nintendo DS.
Hold "Down" and "X" simultaneously, and then press the "L" shoulder button. This resets your Pokewalker back to new.
Tap "Connect to Pokewalker" again, followed by "Save, then go for a Stroll."
Tap the Pokemon you want to transfer to your Pokewalker.
Tap the button on the Pokewalker when prompted. This connects and re-registers your Pokewalker as normal.