We have often read about correctingwhen using images; however all is not lost for JPEGers. This will work best and maybe only on under-exposed images; that is, images that look dark and have not received enough .
With your image open go image>adjustment> (down near the bottom) and there are three sliders to play with. Fiddle with those until you get a more acceptable image. It can also be added from the layers pallet. As usually, work ONLY on a copy of the image
Also handy is shadow/hight control; go image>adjustment>shadow/highlight (just above .
Maybe not be as good as the perfectly exposed image from the camera but it may help you.
I have included an image I mucked up a few years ago with a D100; this only shows correction, more work is required on the image.
You are welcome to add your ideas or more detailed use to this thread; and the Rick may move the thread to a more appropriate forum.