[Theme: Absolum] Title attribute in navigation menu

This is the code of nav-menu:

<div id="nav-back">
		<div id="access" role="navigation">

			<?php wp_nav_menu( array( 'container_class' => 'menu-header', 'theme_location' => 'primary', 'link_before' => '<span class=item-left ></span><span class=icon >' , 'link_after' => '</span><span class=item-right ></span>' ) ); ?>
			</div><!-- #access -->
      </div>

How can i set alt attribute?

https://www.ads-software.com/extend/themes/absolum/