Hello,
Dark patches due to sun exposure or tanning in simple language can be treated and you can get rid of it as tanning is epidermal or superficial as can be treated by clinical exfoliation treatments and creams but its deep dermal then we need to rule out the cause first and treat accordingly and best works for dermal pigmentation is Q switched laser treatments
Next Steps
Kindly share your pictures of your patch so as to diagnose your skin condition and treat it accordingly and consult me via practo pro to know about treatment as well as expert tested DIYs