Try
$globalres="";
add_action('quiz_completed', 'mi_ld_quiz_ert', 10, 2);
function mi_ld_quiz_ert( $quizdata, $current_user ) {
global $globalres;
if($globalres== 0){
do_action('ld_update_group_access', $current_user, 2, $remove = false ));
}
else{
do_action('ld_update_group_access', $current_user, 14, $remove = false ));
}
}
add_action('learndash_ques_single_answer_correct', 'my_ld_quiz_resp',5,5);
function my_ld_quiz_resp( $answerIndex, $correctAnswer, $userResponse) {
global $globalres;
$globalres = $answerIndex;
}