How do you get Articuno in blue rescue team?

You can't actually get Articuno in Pokémon Mystery Dungeon: Blue Rescue Team.

While Articuno is a Legendary Pokémon, it's not available in the game. The only Legendary Pokémon available in Blue Rescue Team are:

* Raikou

* Entei

* Suicune

* Lugia

* Ho-Oh

These Pokémon are obtained through specific events and challenges within the game.

Perhaps you're thinking of a different Pokémon Mystery Dungeon game, like Pokémon Mystery Dungeon: Explorers of Time/Darkness/Sky, where Articuno can be obtained via the post-game content.