I guess that on your original you will have much more information at your disposal vs the limited size that the forum allows.
Another way you might want to look at:
- As there seems to be very little, if any usable information in the Red channel this should be minimised and although I think this could be accomplished using Apply Image I tried using Channel Mixer adjustment
- Select the blue stain area with the masking tool of your choice - I just used quick mask
- Select a Channel Mixer adjustment layer. Check Monochrome and adjust the RGB sliders to get a suitable geryscale image of the stained area. My figures for this were R=-89%, G=+113%, B=107%(do not worry about colour changes at this time). Note: This exceeds the rec. for keeping the total to 100% in Channel Mixer.
- Add another channel mixer adjustment and select Monochrome.
- You should now be able to adjust both Channel Mixer layers to play with the overall effect.
- You will of course need to deal with the ring around left by the stain masking. For this I just used patch tool
The face in particular will need some refinement to get rid of the noise and of course the other general retouching, tonal work that needs to be done