What is an "author's novelty file" in journals? Recently I submitted a paper in a journal then after a few days I got following comments:

Your submission of the manuscript  has been unsubmitted. This is because your "Author's Novelty File" was not detailed enough. In order to proceed, please briefly describe, in a few lines, the new contributions of your paper to the field. Do not repeat for this purpose the content of your abstract. Instead, provide a brief itemized list of these contributions in a separate file.

I don't understand what I have to write now. What he is asking for? I need help with this.

Thanks for giving me time.
It sounds like the journal wants you to identify in what manner your paper has expanded the state of knowledge in your field. Have you contributed a new experimental method? Or perhaps you've provided new insights into some sort of phenomenon, or measured data for a new material, or so on. These contributions should be collected in this "novelty file."