reset engine light

    I went to the zone to have the codes brought up for a 99 malibu. It was showing the fuel evap system. I think my wife is having trouble with the fuel cap again. Anyway they won't reset the computer anymore and told me to just unhook the negative cable, remove/ reinstall the cap a few times and hook the negative cable back up. I have tried this several time and the check engine light won't go out. Is there another way to reset this thing? 

AUTO ZONE CAN ALSO RESET THE CODE, My 98 did this about once a month, P0440 code, and i never did find the cause, but it ran fine, I just reset it when it ocurred