<?php
$dizi =  Array(
    Array(
        3456,
        2345
),
Array(
    5687,
    8956
)
);
$yeni_dizi = array();
foreach($dizi as $key => $value) {
    $yeni_dizi[$key][] = $value[0].' - '.$value[1];

}
echo '<pre>';
print_r($yeni_dizi);
?>