I’m really sorry about that, but you saw the demo website of the theme and saw what the theme can do and what not. Customizable means always that you can change colors, backgrounds, widgets. It does not mean that the theme makes it possible for you to change WordPress functions with just some clicks. The search function is a WordPress core function and was used from the theme. It’s nothing that comes with the theme.
What you want to do are really heavy changes, and it’s not possible to do that with some clicks. If you want, you can contact our developer team (info @ 7theme . net ) and ask for a quote to write a plugin or extension for the search function.