How to Call the Generated file of filesaver.js into the backend code

Question

I used filesaver.js to allow me to download the file successfully.

var out = doc.getZip().generate({
type: "blob",
mimeType: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
}) //Output the document using Data-URI
saveAs(out,"Details.docx");

I need to call the downloaded file into backend code to save the file in S3 Bucket.

I'd be grateful for getting any assistance.