Customers usually will not be able to delete any file if the application is not developed in any of the instances. The below method illustrates how to delete the file from the scoped application using the XML file. Please note this is one of the methods of deletion.
1. Export XML the file(s) you wanted to delete.
2. Open the XML file downloaded.
3. Update the action from "INSERT or UPDATE" to "DELETE".
4. Save the XML file(s).
5. Import XML the same file from any list-layout to delete the file(s).