- var_dump: documentation ( source)
- array_column: documentation ( source)
- array_search: documentation ( source)
<?php
$objs = [ ['value'=>2, 'key'=>'a'], ['value'=>3, 'key'=>'b'] ];
$keys = array_column($objs, 'key');
$index = array_search('c', $keys);
$objs[$index]['key'] = 5;
var_dump($objs);