previewfile - path to the preview file.
Without this field, previously uploaded item files to the workshop will remain the same. You can find it out, for example, by going to the page of a previously uploaded item and copying from the address the number in place XXXXX. You can find it out, for example, by going to the game page and copying from the address the number in place XXXXX.
Where instead of ellipsis, you should enter the fields:
