walker.php

<?php
// Only keep the remove_action that applies to your navigation position set in the Customizer
// Delete the other remove_action calls that don't apply

add_action('after_setup_theme','generate_custom_remove_nav');
function generate_custom_remove_nav() {
	// Above header
	remove_action( 'generate_before_header', 'generate_walker_navigation_position', 5 );
	
	// Float right
	remove_action( 'generate_before_header_content', 'generate_walker_navigation_position', 5 );
	
	// Below header
	remove_action( 'generate_after_header', 'generate_walker_navigation_position', 5 );
}

// Choose the hook below that you have set in the Customizer - very important
// Remove the other add_action calls you don't use

// Above header
add_action( 'generate_before_header', 'generate_walker_navigation_position', 5 );

// Float right
add_action( 'generate_before_header_content', 'generate_walker_navigation_position', 5 );

// Below header
add_action( 'generate_after_header', 'generate_walker_navigation_position', 5 );

// Your new navigation with the Walker
function generate_walker_navigation_position()
{
	?>
	<nav itemtype="http://schema.org/SiteNavigationElement" itemscope="itemscope" id="site-navigation" role="navigation" <?php generate_navigation_class(); ?>>
		<div class="inside-navigation grid-container grid-parent">
			<?php do_action('generate_inside_navigation'); ?>
			<h3 class="menu-toggle"><?php _e( 'Menu', 'generate' ); ?></h3>
			<div class="screen-reader-text skip-link"><a href="#content" title="<?php esc_attr_e( 'Skip to content', 'generate' ); ?>"><?php _e( 'Skip to content', 'generate' ); ?></a></div>
			<?php 
			wp_nav_menu( 
				array( 
					'theme_location' => 'primary',
					'container' => 'div',
					'container_class' => 'main-nav',
					'menu_class' => '',
					'fallback_cb' => 'generate_menu_fallback',
					'items_wrap' => '<ul id="%1$s" class="%2$s ' . join( ' ', generate_get_menu_class() ) . '">%3$s</ul>',
					'walker' => new Your_New_Walker()
				) 
			);
			?>
		</div><!-- .inside-navigation -->
	</nav><!-- #site-navigation -->
	<?php
}