koel/app/Http/Requests/API/UserUpdateRequest.php

<?php

namespace App\Http\Requests\API;

class UserUpdateRequest extends Request
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return auth()->user()->is_admin;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'name' => 'required',
            'email' => 'required|email|unique:users,email,'.$this->route('user')->id,
        ];
    }
}