request()->request->add(['index'=>'value']);
//this is my code
this how to add single attribute to the request object in laravel:-
$request->request->add(['car' => 'value']);
this is how to add multiple attributes to the request object in laravel:-
$request->request->add(['car' => 'value', 'end' => 'done']);
$request->request->add(['variable' => 'value']); //add request
$request->all() + ['index' => 'value'];