Considerations for bulk uploading media files
You can use the import feature as a bulk uploader for media fields. If you provide externally available urls as the value (full HTTP/HTTPS url, publicly available), the media will be copied to ACF's secure Google Cloud Platform bucket and the new url to the uploaded media will be stored in the corresponding metafield.
If you want to delete a media, clear the field's value in the import file.
This applies to both Media v1 and Media v2 field types.