Override Primary Menu via Child Theme

Greetings! Great theme. Once the client approves the look for their website, we will be purchasing the Pro version. In the meantime, I have been doing prep work. The client requests we keep the original top-navigation. So, I created a child theme, duplicated what was necessary, and replaced the Primary Menu code with a "require_once" statement. Problem is the child theme does not override the parent theme. I have tried the usual techniques (e.g., pluggable functions, function priority, and removing original hooks). None of them work. I tried different variations, like priority numbers, hook callouts (e.g., wp_loaded, init, clean_education_header, clean_education_after_header, etc.). Still no luck. Here's the parent and child theme code I am working with. Some help is greatly appreciated. Thanks in advance. Parent Theme:

if ( ! function_exists( 'clean_education_primary_menu' ) ) :
    function clean_education_primary_menu() {
        ?>
        <button id="menu-toggle-primary" class="menu-toggle"><?php esc_html_e( 'Menu', 'clean-education' ); ?></button>

        <div id="site-header-menu-primary" class="site-header-menu">
                <nav id="site-navigation-primary" class="main-navigation" role="navigation" aria-label="<?php esc_attr_e( 'Primary Menu', 'clean-education' ); ?>">
                <h3 class="screen-reader-text"><?php _e( 'Primary menu', 'clean-education' ); ?></h3>
                    <?php
                        if ( has_nav_menu( 'primary' ) ) {
                            $args = array(
                                'theme_location'    => 'primary',
                                'menu_class'        => 'menu primary-menu',
                                'container'         => false
                            );
                            wp_nav_menu( $args );
                        }
                        else {
                            wp_page_menu( array( 'menu_class'  => 'default-page-menu' ) );
                        }
                    ?>
                </nav><!-- .main-navigation -->
        </div><!-- .site-header-menu -->
    <?php
    }
endif;
add_action( 'clean_education_header', 'clean_education_primary_menu', 60 );

Child Theme:

    function clean_education_primary_menu() {
        ?>
        <button id="menu-toggle-primary" class="menu-toggle"><?php esc_html_e( 'Menu', 'clean-education' ); ?></button>

        <div id="site-header-menu-primary" class="site-header-menu">
                <nav id="site-navigation-primary" class="main-navigation" role="navigation" aria-label="<?php esc_attr_e( 'Primary Menu', 'clean-education' ); ?>">
                <h3 class="screen-reader-text"><?php _e( 'Primary menu', 'clean-education' ); ?></h3>
                    <?php require_once('topnav.php'); ?>
                </nav><!-- .main-navigation -->
        </div><!-- .site-header-menu -->
    <?php
    }
add_action( 'clean_education_header', 'clean_education_primary_menu', 65 );
function child_remove_parent_function() {
    remove_action( 'clean_education_header', 'clean_education_primary_menu', 60 );
}
add_action( 'wp_loaded', 'child_remove_parent_function' );