I am going to assuming that you have a button that looks like this:

<a class="my-link" href="#my-visual-composer-row-id">Click here to scroll down</a>

and I am going to assume that you have given your visual composer row an ID of my-visual-composer-row-id (you can do this under the edit options on the actual row itself)

If you’re ok with using jQuery, you can then implement the following either in a RAW JavaScript block somewhere (preferably the bottom of the page), or if you’re making your own theme, you can add this to your .js file.

jQuery(document).ready(function($){
    $('.my-link, .my-link a').click(function(e){
        if (location.pathname.replace(/^\//,'') == this.pathname.replace(/^\//,'') && location.hostname == this.hostname) {
            var target = jQuery(this.hash);
            target = target.length ? target : jQuery('[name=' + this.hash.slice(1) +']');
            if (target.length) {
                jQuery('html, body').animate({
                    scrollTop: Math.ceil(target.offset().top) 
                }, 1000);
            return false;
            }
        }
    });
});

Source: here