Form UI in Command

<?php

namespace:

use pocketmine\plugin\PluginManager;
use pocketmine\server;
use pocketmine\player;
use pocketmine\plugin\PluginBase;
use pocketmine\event\Listener;
use pocketmine\command\command;
use pocketmine\command\commandsender;
use pocketmine\event\Player\playerJoinEvent;
use pocketmine\event\player\PlayerQuitEvent;
use pocketmine\utils\TextFormat;

class Main extends pluginbase implements listener
	{
	public function onCommand(CommandSender $sender, Command $cmd, string $label, array $args): bool
    {
        switch ($cmd->getName()) {
            case "FFA":
                if ($sender instanceof Player) {
                    //real player
                    $this->openMyForm($sender);
                }
                break;
        }
        return true;
    }
	}