It's impossible for anyone to help you without knowing a lot more about how your site is set up.
Firstly, what e-commerce plugin are you using? That's the main thing that is needed because they all do things in different ways.
And... If it's that urgent you may want to consider hiring someone to help. This is a volunteer run forum, so even though we all try to help as much as possible there's no guarantee that you'll find someone that can give you a specific answer.