Cannot change the data of the $request

[MahbodHastam]

Hi, I have the request validation:

$request->validate([
    'image' => 'required|file|mimes:png,jpg,jpeg',
]);

And I want to merge it with the path of the uploaded image:

$request->merge(['image' => $image]);

But it's not working! And when I dd the $request->all(), it shows me the instance of Illuminate\Http\UploadedFile again.

What do I have to do?
That's not a serious problem and it can be solved with other methods but I want to know what's the problem with the request?