I would be pleased to answer your question .
You will need to apply a lightening agent . The best to apply on that dark spot is a Vitamin C
serum which is safe and effective and will not cause any increase in the sensitivity of the skin .
Please note : putting creams ( containing triple combination of steroids and hydroquinone
) under the lip area can make the skin very sensitive.
Hence the above regime is suggested .
You can get Vitamin C prescribed from your Dermatologist
Thanks and Take care