MelancholyElk85

How do I add files without uploading them anywhere?

The files themselves need to be packaged into a zip file (so we have an immutable copy of the dataset). This means you cannot "register" existing files (in your example, files on your S3 bucket?!). The idea is to make sure your dataset is protected against changes on the one hand, but on the other to allow you to change it, and only store the changeset.
Does that make sense ?