Hi,

When you customize the odoo using the odoo studio, it will not be there under the Apps menu as and app, instead it will be creating records under the Menu, Views etc, based on what you are doing.

The app you referred to in the question will be a main menu, and you can see it, if you navigate to Settings -> Technical -> User Interface -> Menu Items. You can delete the menu from here if you don't need it again. Also if you need to delete other related records like view, you can delete it from the Views menu under the User Interface menu under the settings-> technical.

Thanks