how to change default laravel unique error me code example

Example 1: how to add an custom error to validater error in laravel

if (request('event') == null) {
    $validator->errors()->add('event', 'Please select an event');
}

Example 2: laravel custom validation message

$rules = [
        'name' => 'required',
        'email' => 'required|email',
        'message' => 'required|max:250',
    ];

    $customMessages = [
        'required' => 'The :attribute field is required.'
    ];

    $this->validate($request, $rules, $customMessages);