If You look at
https://www.smartmenus.org/docs/#styling-menus (there : smalll screen devices) You find a code with
<!– Mobile menu toggle button (hamburger/x icon) –>
<input id=”main-menu-state” type=”checkbox” />
<label class=”main-menu-btn” for=”main-menu-state”>
<span class=”main-menu-btn-icon”></span> Toggle main menu visibility
</label>
<h2 class=”nav-brand”>Brand</h2>
which You can put into the footer (together with the js)
At https://www.smartmenus.org/about/themes/ You just have to shift the page together into narrow mode and then the button appears in the top nav-line.
an example is at
https://jsfiddle.net/vadikom/oxe40pat/?utm_source=website&utm_medium=embed&utm_campaign=oxe40pat
This will function with some modifications.