function custom_setup_nav() {
  global $bp;

  bp_core_new_nav_item( array(
        'name' => __( 'About', 'buddypress' ),
        'slug' => 'about',
        'position' => 30,
        'screen_function' => 'about_page'
  ) );
}

add_action( 'bp_setup_nav', 'custom_setup_nav' );

function about_page() {
bp_core_load_template( apply_filters( 'bp_core_template_plugin', 'members/single/about' ) );
}