Hi Dear,
I can understand your problem. Prolonged use of masks have been widely seen to be causing damage to skin. Most commonly affecting the nasal bridge and cheeks on the zygomatic bone at the point of contact with the mask. This may be due to the compression of the adjustable nose-clip portion of the mask, exposure to more pressure because the nasal bridge area isare more prominent, and the relatively thin skin in these areas.
You can apply Vaseline/Pure coconut oil (no added medication) and massage gently for a while. This should be done on daily. It will lighten the pigmentation.
Next Steps
If it doesnt give relief then go for Homoeopathic treatment.
Health Tips
Please be gentle while doing massage don't over do. Also apply moisturizer on the nose before wearing Mask.