Use this code example to mark every quiz answer, no matter what it is, as being scored correct.

add_filter( 'frm_quiz_is_correct', '__return_true' );

Use this code example to mark all answers as wrong, even ones that are right.

add_filter( 'frm_quiz_is_correct', '__return_false' );

Use this code example to check for a specific field and mark it as always correct.

add_filter( 'frm_quiz_is_correct', 'is_quiz_correct', 10, 2 );
function is_quiz_correct( $is_correct, $args ) {
	$target_field_id = 1246; // Change 1246 with your field ID
	if ( $target_field_id === (int) $args['field']->id ) {
		$is_correct = true;
	}
	return $is_correct;
}

Use this to check for a specific field and mark it as always correct. This code example adds an extra check so it would only change the is_correct value when the answer is Alternative answer. e.g. you have two right answers.

add_filter( 'frm_quiz_is_correct', 'is_quiz_correct', 10, 2 );
function is_quiz_correct( $is_correct, $args ) {
	$target_field_id = 1246; // Change 1246 with your field ID
	if ( $target_field_id === (int) $args['field']->id && 'Alternative answer' === $args['value'] ) { // Change the text for 'Alternative answer'
		$is_correct = true;
	}
	return $is_correct;
}