Well, this is a tough one for us :((. These are steps to make sure that uninstalling Flash search app is almost as easy as installing.
Take backups before installing the app. Having the option of going back in time that you should be able to done. Please go to Customization -> Find the theme that you want to backup, and then click Actions -> Export.
Before uninstalling the app, this is what needs to be done to delete it completely. From your Flash search admin, go to Installation -> Themes. Select the theme then click Actions -> Uninstall layout.
Click Uninstall, it will take a few minutes to complete the process.
Shopify Online Store 2.0 Theme:
From your Shopify admin, go to Apps -> then click delete app.
So above is a guide on how to uninstall app. As easy as it seems, uninstalling the app does present some challenges, though they can be overcome if handled with care and an open mind.