The data-sticky attribute controls whether the secondary nav will stick to the to top of the screen (or bottom of your header). This setting is only applicable when used with the data-position="bottom" attribute.
<div data-wm-plugin="subnav"
data-sticky="true">
</div>
You may want to add the below code to your Custom CSS area to ensure the Sticky Navigation sits on top of all other elements on your page, and nothing accidentally overlaps it.
.sticky-page-section {
z-index: 9999 !important;
}