Change array in config?

[h4yfans]

I have a code line like this in my config file.

'locales' => [
        'en',
        'fr',
        'es' => [
            'MX', // mexican spanish
            'CO', // colombian spanish
        ],
    ],

I want to change with this.

'locales' => [
          'tr',
          'en',
],

 $newArr = [
'en',
'tr'
]

When I try $config->set('locales, $newArr'); I getting error.
Unable to rewrite key "locales.1" in config, rewrite failed