How do you get to four island in Pokemon FireRed?

You can't get to Four Island in Pokemon FireRed! Four Island is exclusive to Pokemon Emerald.

Here's why:

* Different Regions: FireRed takes place in the Kanto region, while Emerald takes place in the Hoenn region. Four Island is located in the Hoenn region.

* Different Storylines: The games have different storylines, and the inclusion of Four Island is specific to the Emerald storyline.

To experience Four Island, you'll need to play Pokemon Emerald.