Outdoor activities make our skin tan. The only option is to wear protective full sleeves clothing and cover as much as possible. Usage of a cap or hat and umbrella is encouraged. Skin already tanned can be treated with de-pigmenting creams and other oral medications. A good skin care regimen comprises 4 steps - cleansing, toning, moisturizing and sun block. Based on your skin type, a dermatologist will recommend you appropriate products. Protect your feet by wearing shoes to the office. Tan will dilute and disappear.
You can start on a mild topical retinoid till you meet a Dermatologist on the feet.
You can consult me on Practo Direct for personal recommendations.