You cannot upload label files yourself. This has to be done by us. Once we have uploaded the files you will receive an email request to approve the files from within your account. The labels will not be released to any orders you place until they have been approved within your account.
You can send your files direct to our design team at design@nutribl.com. To avoid any file integrity issues while sending them to us, we suggest either sending them in a zip folder or using a file transfer service such as We Transfer - https://wetransfer.com