How to add and update config varaibles in laravel

I have a config variable file which I'm using it in my controllers instead of mysql for faster performance.

But my problem is that I can only read from this config file and I can not add or update any value from it.

any suggestion how to udpate or add new values to this variable file :

my variable file which is stored in /config/Banners_size.php:

return [
    "normal_x970h90" => [
        'status' => 'enable',
        'value' => '500'
    ],

    "normal_x234h60" => [
        'status' => 'enable',
        'value' => '500'
    ],
]

my php code to add new array to it which is not working :

    $banners = Config('Banners_size');
    $banner = array($request->input('size')=>['status'=>$request->input('status'),'value'=>$request->input('cost')]);

   $bannerinfo = array_merge($banners, $banner);

    Config('Banners_size' , $bannerinfo);