Canon PowerShot S120 Manual (en)

Select a point that is to be the standard for white 
balance in the shot image, and register the white 
balance in the camera.
Click the [
] button, and in the displayed image in step 1, 
click on a point that is to be the standard for white balance with 
the mouse.
The white balance is registered to the destination selected in 
step 2, and applied to displayed images.
Click [
] again to exit the function.