How do you get to Kanto on soul silver?

To get to Kanto in Pokemon Soul Silver, you must first have completed the main story of the game and have defeated Red at the top of Mt. Silver after completing the Kanto Johto Pokemon league (which includes beating gyms on both regions and then defeating the Elite Four). Once you've done so, you'll be able to access Kanto by talking to Professor Oak in his lab in Pallet Town. He will give you the Pokedex and send you on your journey to explore Kanto.