Hi mark835
Thanks for contacting us.
Please install and activate the Code Snippets plugin.
After creating the new snippets paste the below code.
add_filter( 'get_custom_logo', 'wecodeart_com' );
function wecodeart_com() {
    $custom_logo_id = get_theme_mod( 'custom_logo' );
    $html = sprintf( '<a href="%1$s" class="custom-logo-link" rel="home" itemprop="url">%2$s</a>',
            esc_url( 'www.google.com' ),
            wp_get_attachment_image( $custom_logo_id, 'full', false, array(
                'class'    => 'custom-logo',
            ) )
        );
    return $html;   
} 
For more help see the screenshot http://prntscr.com/tzxsa1
Now check your site and let us know if it works.
Thanks