This article explains how to replace the native search bar in the Cartzilla theme by MadrasThemes
The FiboSearch plugin features built-in integration with this theme. It means you can replace the default search bars by selecting a single checkbox.
If you have activated the Cartzilla theme or the child theme of the Cartzilla theme, you should see the following screen in the plugin settings:
Select the option Replace them and the search bar should be replaced.