On your AppScenic Account, go to Import Products, then Online Feeds.
Now find the feed/file you want to clone or duplicate.
Click on the Actions button on the other side of that file.
Choose Duplicate and then confirm your choice on the pop-up window.
And you are all set!
Now you only need to edit or update your feed by following the same steps like the ones for creating a New Feed.
If you don't remember how to do that, check these steps here.
And this is how you duplicate an online feed.