You can do this in person at if you live in one of their tour cities, or mail your old mascara in with the form that you print off. I got an error when I tried to open the form, though. I have had luck with their customer service people, though, so I'm going to hunt down the number and give them a call to see if they can send a form fix the link.
http://covergirl.com/cgcollection/ey...t/finder.jhtml