WP Front Scroll Top is a nice button that express scrolls up. Smooth Scroll is a less attractive set of buttons that local- and express-scroll up and local-scroll down. Both work very nicely. But is there anything that does express-scroll down? I can’t find anything. Not vital, but hope springs . . .
You might take a look at the Page scroll to id plugin. It works a little differently, because you’ll first create an anchor anywhere on your page. Then, you’ll create a link to that anchor. And when your site visitors click the link, the page will scroll smoothly to the anchor.
You can see this in action on our homepage, in fact. Select the large, green button labeled, “Start Learning Now” and your browser will smoothly scroll down to the pricing table at the bottom of the homepage.
Be sure to view the tutorial in the plugin’s detail page, linked above.
Hope this helps!