No tool fixes a backlit subject faster than Shadow/Highlight, which corrects the too-dark shadows and can even darken highlights when they're overly bright.
1. Get the Shadow/Highlight tool by going to Image > Adjustments > Shadow/Highlight.
2. Move the Shadows slider right: The default value of 50% is good, but pushing it up to 72% is better.
3. Add some tone back into the highlights by moving the Highlights slider right, to about 7%. This will even out the picture's tone. Click OK, and you're all set.