OK. Take the black one ( I hope you have quite big piece of it. Put it on a flat surface like in the first pic below.
Then holding with right hand by the one of the sheet corner, sand the card with left hand moving it around like in the second pic. Sand both side.
OK. Keep sanding . Both sides have to be white like the snow. I know it is quite hard to do that for you but the CA glue doesn't like a such kind paint on these cards.As a result it can peel off and the work is for nothing.