How to remove white birthmarks?

Unlikely to happen. White birthmarks generally reflect an absence or decreased production of pigment in the patch of skin involved.This cannot be reversed. In theory you could transplant a full thickness graft of your skin to cover the area, but it would never look "normal" and would have some visible demarcation at the edges that would call attention to the patch.Most would use a cover makeup for prominent areas.
Show it to your. Pediatrician to determine if you need to see a dermatologist or other specialist. Your description in " conditions"'is incomplete, so i don't know what it stretches across. There are several causes of localized areas of hypopigmentation (white lines or patches). Some of them are important while others are just annoying. A dermatologist will know which make-up provides the best coverage.