3 step technique to open up the left
1. I copied the image to it's own layer and removed the background layer
2. added a levels adjustment and moved the middle input slider to the left to open up the left side of the photo. At this point the entire image will brighten up.
3. enter the layer mask. add the layer mask on the levels adjustment layer you just created and create a black and white gradient horizontally. just make sure the gradient is white on the left and black on the right as the white areas will reveal the levels adjustment and the black areas will hide the levels adjustment. this allows you to selectively open up your image. if you need to fine tune the gradient keep this in mind:
the length of the gradient line that you drag determines how the gradient progresses (short lines = harsh change from black to white, a longer drag = smoother transition)
i started my gradient left of the horizontal center and dragged about 2 inches to the left. I didn't want a harsh transition or a super smooth one because the problem area wasn't abrupt but it also wasn't that gradual. e.g. match the gradient to the nature of the problem.