i quick way to get it close so its easier to clone is.
1. first roughly select around the light area
2. copy/paste the selection
3. then select an area of the pants that are dark
4. copy and paste that selection (place it above the light selection layer)
5. move it so it covers the light part then keep duplicating and moving that layer until all light area is fully covered
6. merge all those dark layers together
7. blur that layer a bit so pattern of pants arent visible
8. make a selection of the BG of the light layer then select the dark layer and delete (so the dark selection is the same size as the light part)
9. change the dark layer blend mode to color
10. merge the dark and light layer
11. then duplicate that layer and change the blend mode to "Multiply"
12. erase the edges as close as the light area as you can
13. do some master Hue/Sateration on that layer. (lower the light to about -15 and increase saturation to about 35) that should get you close to the result your after then just heal the edges
here is my result
