unserialize() function is used to serialized string into its original form. 

<?php
$serializedData = 'a:3:{s:4:"name";s:4:"John";s:3:"age";i:30;s:4:"city";s:8:"New York";}';
$data = unserialize($serializedData);
print_r($data);
?>

Output:

Array
(
   [name] => John
   [age] => 30
   [city] => New York
)