Hi Julia,
as you have uploaded your application as an App Project application, you are not allowed to import an application with the same name via the Catalog again.
To clarify, the error message "Application name already exists" directly indicates that there is another application installed on your IEM, but with a distinct application ID.
If your intention is to upload an updated version of the same application, it's important to ensure that you create a new version specific to that particular app. The related iectl command can be located in the documentation.
App Project apps vs. Catalog apps:
You need to consider your app type when uploading your app the first time.