Thanks for the query.
Dark lips are inherent and difficult to treat.
There are various modalities but the result is not that great.
However you can give a trial.
Use a mild depigmenting agent like melaglow in night.
In morning you can apply a mild steroid like mometasone
Later in the day use lip balms, containing sunscreen.
Peels are also a good option.
You can go for milder peels like lactic acid, once a month.
Also take an antioxidant capsule daily.
Depiwhite may help you, but dont continue it for long, it has steroids
Let me know if you have any other doubts.