you cant. you're born with it
make up or ice.
Why would you want to get rid of lip and mouth cancers - aren't they cute. STOP SMOKING!
How fond of your lip are you? You need to get rid of the piercing and get some antibiotics from your doctor and stop doing goofy stuff like that.
If you are a women or girl try wearing lip gloss or lipstick. If you are a boy or a man than try using chapstick; the dark kind, maybe like burts bees.
I can't say I ever had a black line on my nintendo 3ds, but bring it to your local game store, they should be able to help.
Try using ice
use a screw driver
you can use coco butter
use salicylic acid on the spots and exfoliate gently
put on lots of lip care and drink water and don't lick your lips
clean it everyday with H2ocean and go to the hospital
Make Sure you keep it clean with mouthwash and salt water