I want that my app can generate a unique link wich every time downloads the last file uploaded on the database when clicked.
Just create a JS query that first retrieves the latest file from your DB and then exports it.
You wouldn't need a link per-se for this but a button that triggers the query. If you need a public facing link you could create a public app that triggers these queries on page load.
If you share a bit more on your set up we can help out more :))