dependant list box country and city

i am developing a website containing a registration page which contain a city and country list box and have a database populate it with country and city and the dependant list box work well . but on other page editing page , we should display to the user the city that the user selected and this point not working with me i could not display the option that the user select, may be because the city file just call when the user made a change on the country list box