1.If you have installed Facebook app on your device:

When you tap Switch Account in the game, you will go to Facebook app in your device. Tap Continue to enter the game account that is buond to the Facebook account. If you want to switch to another game account, you need to log out the current Facebook account in the Facebook app. Log into the Facebook account to which that game is bound, and then enter the game to switch game.

2.If you haven't installed Facebook app on your device:

Tap Switch Account > Facebook Account in the game and the Facebook interface on the browser would pops up. Tap Contine to switch to the game account that is bound to current Facebook account. If you want to switch to another game account, you need to tap Cancel button on the Facebook interface and go back to Switch Account interface to switch account again.