$actions = array(
    array('action' => 'Action1', 'value' => '0'),
    array('action' => 'Action2', 'value' => '0'),
);

foreach($actions as $item){
    if($item['action'] == 'Action1'){
        $item['value'] = 20;
    }
}

foreach ($actions as &$item) {
}

foreach($actions as $key => $val){
    if($val['action'] == 'Action1'){
        $actions[$key]['value'] = 20;
    }
}

foreach($actions as &$item){    //<== add "&" reference to the $item that now when ever you change it the actions will change
    if($item['action'] == 'Action1'){
        $item['value'] = 20;
    }
}

foreach($actions as $key => $item){
    if($item['action'] == 'Action1'){
        $actions[$key]['value'] = 20; // directly access $action and modify the value
    }
}

foreach(array_keys($actions) as $key){
    $item = &$actions[$key];
    if($item['action'] == 'Action1'){
        $item['value'] = 20;
    }
}

foreach($actions as &$item)