What do you after defeat all the Kanto gyms in Pokemon soulsilver?

1. Go to the Pokémon League on Route 23 to challenge the Elite Four and the Pokémon League Champion.

2. You must defeat the Elite Four in order to gain access to the Champion.

3. After you defeat the Champion, you will officially become the new Champion of the Pokémon League and will unlock the National Dex.

4. You can now continue to explore the Kanto region, catch more Pokémon, and complete side quests.

5. Some post game questlines will appear, like for example catching the three legendary dogs.