I used Kojie San Soap on my knees. One is lighter than the other. What can I do to fix this? (Photo)

Thank you for your question and posting a picture.  It looks like you might have Post Inflammatory Hyperpigmentation (PIH).  This obviously related to the LHR.  It looks like they were too aggressive on the settings.  You should speak to their supervising physician to see what they recommend.We have been very successful using the PicoSure laser with the FOCUS and / or Flat Lenses eliminating hyperpigmentation with a series of treatments.  FOCUS lens treatments have the extra benefit of reducing fine lines and wrinkles.  This is one of our go to treatments for patients older than 40 and worried about the signs of aging.  This laser is safe for all skin types.  Start with sunscreen every day!  Once you have treated your hyperpigmentation to your satisfaction, you will probably need a follow treatment every 6 to 12 months depending your level of re-pigmentation.  Best of luck.