add_action( 'ld_added_group_access', 'my_add_group_access', 10, 2 );

function my_add_group_access( $user_id, $group_id ) {

    $settings = get_post_meta( $group_id, 'wpf-settings-learndash', true );

    if(empty($settings) || empty($settings['tag_link']))
        return;

    wp_fusion()->user->apply_tags( $settings['tag_link'], $user_id );

}

add_action( 'ld_removed_group_access', 'my_remove_group_access', 10, 2 );

function my_remove_group_access( $user_id, $group_id ) {

    $settings = get_post_meta( $group_id, 'wpf-settings-learndash', true );

    if(empty($settings) || empty($settings['tag_link']))
        return;

    wp_fusion()->user->remove_tags( $settings['tag_link'], $user_id );

}