THIS DOES NOT WORK FOR GETTING MARKER OFF OF THE LABELS!!! That is basically permanent, and I do not recommend attempting to remove marker from the label, short of removing the label and replacing it.
Get some materials. You'll need: Paper towels, and you can use either isopropyl (rubbing) alcohol, or you can use Clorox wipes. Check that the Clorox wipes do not contain bleach.
If the marker is near the label, take some caution in how much cleaner you use. Don't go crazy, it doesn't take a lot to remove it. Use a paper towel and hold it over the label while you are cleaning. Also, cover the cartridge opening if the marker is near the opening.
Wet a paper towel or grab a wipe and begin scrubbing. Push hard enough to remove the marker, but don't push so hard the paper towel begins to rip. If you are using a Clorox wipe, the soap that is on the cartridge should turn black.
Wipe any solution off the cartridge. The marker should start lightening.
Keep cleaning until the marker gets very faint.
Once the marker gets extremely faint, to the point where you need to really look for it to see it, you are almost done.
At this point, you can begin pushing hard enough to fray the paper towel. The cartridge should not feel as if it is breaking or being crushed. The paper towel also should not rip.