Its all in the tiitle
Pleaselog inorregisterto add a comment.
You need a gracidia flower to change shaymin.
PS it needs to be the event shaymin with the fateful enounter in it’s summary
Use a Gracidea Flower on it during the day.>While it is not known to evolve into or from another Pokémon, it has a second Forme activated by using a Gracidea flower in the daytime. Its original Forme, Land Forme, will then become Sky Forme. -Bulbapedia
The Gracidea Flower can be found in the Pokemon Center in Lacunosa Town.
You don’t change it in a place. If you have an event Shaymin, take it to Lacunosa Town’s Pokemon Center. Then, talk to the lady inside with Shaymin in front of your party. Then, she’ll give you a Gracidea for Shaymin. Use it on Shaymin to change it into Sky Forme. You can only change it when it is day and Shaymin is not frozen.