You can use the Tone Curve to adjust a picture's overall brightness, color balance, etc. ※This is a premium feature.
Open My Gallery and tap on ① +.
Select the ① Import Picture.
We will be working on this photo since its brightness and color balance is slightly off. Open the ① Tool Selection window and select the ② Filter.
Select the ① Tone Curve.
Adjust the brightness in the ① RGB tab. Drag the ②Knob to adjust the brightness and darkness. You can add more knobs by tapping an empty space if two knobs are not enough.
The right of the graph adjusts the brightness of the highlights. The left of the graph adjusts the brightness of the shadows.
Move the knob up to make it brighter, and down to make it darker.
After the brightness is adjusted, the photo may appear too red or to blue depending on where it was taken. This is due to the Color Balance. If it appears too red, select ① R. Move the curve up to make it more red, or down to make it more blue. In this case we would like to make it less red, so we will drag the ② knob down.
By using the Tone Curve, we have made the brightness and the color of this photo more natural.