<?php

$cars = array(
    array("Volvo" , '22,18,'),
    array("BMW" , '15,13'),
    array("Saab", '5,2' ),
    array("Land Rover", '17,15' )
);

print_r($cars);

$labels = array_column($cars, 0); // Get car manufacturer list
$labels = array_map(function($element){return $element[0];}, $cars);
$id = array_search('Volvo', $labels); // Find id of 'Volvo'
$cars[$id][1].='21,'; //append value
$cars[$id][1].='27,'; //append value

print_r($cars);