Directly to you from Twitter:
Get ready for the new Tempest Trials, starting 6/8! Gather your strongest allies and fight through a series of maps… twitter.com/i/web/status/8…—
Nintendo of America (@NintendoAmerica) June 05, 2017
…Wanna play? Buy a 3DS.
That being said, click on Fire Emblem Heroes for everything you need to know about the game. 😀