Hi 
Thanks for your query
You seem to have developed skin pigmentation due to tanning.
Topical medications can definitely be of help to you in reducing the pigmentation to some extent.
I would advice that you should use a lightening agent like 
kojic acid and 
vitamin c combination over the affected areas. This is a simple, harmless lightening agent which can be used for as long the blackish pigmentation is there. 
Also ,try not to touch the area too much 
Use proper sunscreen (spf>26) before going out in the sun so that the lesion doesn't darken any further 
Take a diet rich in vitamin C and antioxidants like Citrus fruits and lots of salads 
If after all the above measures, the pigmentation tend to persist, then i would advise that you should see a 
dermatologist as there are various other measures for the treatment of pigmented skin like the use of 
chemical peels, 
dermabrasion etc which a dermatologist can decide according to the type of scars.. 
Hope it helps 
Wishing you speedy recovery 
Dr Geetika Paul