Treatment of lightening of the skin on the upper lip depends on the cause. Sometimes it goes away on its own after exposure to the sun but if it due to hypopigmentation causes like vitiligo then it needs specific treatment.
Treatment options for vitiligo include steroids, psoralen photochemotherapy(PUVA), depigmentation and surgical therapy like skin grafting, micropigmentation and autologous melanocyte transplants. But this depends on the area and the cause of this hypopigmentation.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.