Formatting a Carbon date instance

First parse the created_at field as Carbon object.

$createdAt = Carbon::parse($item['created_at']);

Then you can use

$suborder['payment_date'] = $createdAt->format('M d Y');

Date Casting for Laravel 6.x and 7.x

/**
* The attributes that should be cast.
*
* @var array
*/
protected $casts = [
   'created_at' => 'datetime:Y-m-d',
   'updated_at' => 'datetime:Y-m-d',
   'deleted_at' => 'datetime:Y-m-d h:i:s'
];

It easy for Laravel 5 in your Model add property protected $dates = ['created_at', 'cached_at']. See detail here https://laravel.com/docs/5.2/eloquent-mutators#date-mutators

Date Mutators: Laravel 5.x

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
   /**
   * The attributes that should be mutated to dates.
   *
   * @var array
   */
   protected $dates = ['created_at', 'updated_at', 'deleted_at'];
}

You can format date like this $user->created_at->format('M d Y'); or any format that support by PHP.

$suborder['payment_date'] = Carbon::parse($item['created_at'])->format('M d Y');

If you are using eloquent model (by looking at your code, i think you are), you dont need to convert it into array. Just use it as object. Becaus elike Thomas Kim said, by default it is a Carbon instance

So it should be

$suborder['payment_date'] = $item->created_at->format('Y-m-d')

But if it is not then, you need convert it to Carbon object as Milan Maharjan answer

$createdAt = Carbon::parse($item['created_at']);

Declare in model:

class ModelName extends Model
{      

 protected $casts = [
    'created_at' => 'datetime:d/m/Y', // Change your format
    'updated_at' => 'datetime:d/m/Y',
];