In this lesson you can adjust the tonality of the highlight areas without effecting the shadows and mid tones.
If you did the previous step correctly, you will have selected the image as indicated by the marching ants.
If not then repeat on the RGB channel.
Double Click on the Curves icon if the Adjustments panel is not open.
Adjust the Curve up or down to modify the highlights only.
Note the shortened histogram displaying only the highlight area.
Toggle the layer on and off to view the result.