Walkthrough

1. For completing this request, you can get Ditto Flag Recipe as a reward.
2. Talk to Charmander to follow you to Professor Tangrowth
3. After talking to Professor Tangrowth, you will receive the Ditto Flag.
4. Place the Ditto Flag near or on your house. To do this, go to your inventory and select the Ditto Flag.
5. After adding the Ditto Flag, you'll officially own the house, and the next time you start the game, you'll spawn in front of it.

Walkthrough source: Game8.