To improve your tanned skin, you may follow these suggestions
1) use a sunscreen of SPF 50. Apply it 30 minutes prior to going out and should be repeated every two to three hours.
2) take oral vitamin c and antioxidant supplements
3) apply a Kojic acid
or Glycolic acid
cream in morning and hydroquinone
4 percent cream in night. Apply in small amounts, if any irritation develops withhold use.
4) take few sessions of chemical peels
to get your constitutive skin color back.
As these drugs require follow up, kindly be under a doctor's consultation.
Hope that answers your query. Take care.