How do you change shaymin into its sky form in heartgold if got it through AR?

You can't change Shaymin into its Sky Forme in Pokémon HeartGold if you obtained it through AR.

Here's why:

* Shaymin's Sky Forme is tied to a specific event: The only way to get Shaymin in its Sky Forme in HeartGold was through a specific event in 2010, where players could receive a special item called the "Gracidea Flower" and use it on their Shaymin.

* AR Shaymin is a standard form: AR Shaymin is the standard Land Forme, and there is no way to change it within the game itself.

To get Shaymin's Sky Forme in HeartGold, you would have needed to obtain it through the event in 2010.

If you're looking for a Sky Forme Shaymin, you may be able to find one through trading with other players, but unfortunately, you can't obtain it through any means within the game itself.