Rub the marker with rubbing alcohol on a cotton ball or cloth
Wipe with hand sanitizer
Use a dry-erase marker over the permanent marker, then wipe off
Apply acetone or nail polish remover with a cotton swab
Use baking soda mixed with a little water to make a paste
Scrub gently with a magic eraser
Wipe with white vinegar
Use toothpaste on a soft cloth
Wash the plastic with warm soapy water after cleaning
Repeat as needed until the stain is gone