Level 15
I'm assuming this is a custom field (not created_at, updated_at field).
What you can do, is cast the field as date. That will always return a new Carbon instance which you can easily manipulate:
protected $casts = [
YOUR_FIELD_NAME => 'date'
]
Then when you're retrieving the value, just apply the format metho in carbon:
$your_model->date_field->format('Y-m')