Don’t underestimate the power of levels
Sometimes, there’s not enough light to expose the subject. Apply Levels as a new layer and slide the Highlights and Midtones left to correct for the main subject.
Using the Levels adjustment’s mask, paint away the background with a soft brush to reveal the unedited original. You may need to go over the subject’s edges.
Hide the Levels adjustment and locate the Quick Select tool (Q). Select the background around the main subject. Reveal the Levels adjustment and go to Select>Inverse to flip the selection.
Use the Eraser tool (E) to remove excess dark parts over the edges and hit Cmd/Ctrl+D to remove the selection. You should be left with a more balanced exposure. Lower the Levels’ Opacity to suit.