Dealing with product feeds is a bit hard, because of the mapping needed for product attributes.
While we allow to do it through our admin dashboard, requires some technical knowledge of doing it.
If you already have a product feed with the correct mapping and want to update it or to change to a new one, you can use the preview method available under Setup -> Product Feed
By default URL and params from here are copied from default ones. You may play with the feedParams and click Preview without replacing existing products or breaking anything.