In Pokemon fire red How do you go back to Cinnabar island after you get to the ONE ISLAND?

First, go to Two Island, enter the Game Corner, and talk to the man inside. After that, head to Three Island and find Lostelle in the Berry Forest. You'll need to defeat (or catch) a Level 30 Hypno to save her. Once she's safely back at home, you can return to Kanto as soon as you talk to Bill again. Be warned, however: you won't be able to come back to the Sevii Islands until after you defeat the Elite Four.