$factory = \alvin0319\SimpleMapRenderer\MapFactory::getInstance();

$mapId = your_map_id;
$mapData = $factory->getMapData($mapId);

$mapId = your_custom_map_id; 
$colors = [];
$center = new Vector3(0, 0, 0);
for($y = 0; $y < 128; $y++){
    for($x = 0; $x < 128; $x++){
        $colors[] = new \pocketmine\utils\Color(mt_rand(0, 128), mt_rand(0, 128), mt_rand(0, 128));
    }
}
$mapData = new \alvin0319\SimpleMapRenderer\data\MapData($mapId, $colors, false, $center);

$factory->registerData($mapData);

$block = Level->getBlock($x, $y, $z);
$color = \alvin0319\SimpleMapRenderer\util\MapUtil::getMapColorByBlock($block);

$filePath = path_to_your_png_file;
$colors = [];
for($y = 0; $y < 128; $y++){
    for($x = 0; $x < 128; $x++){
        $colors[] = new \pocketmine\utils\Color(mt_rand(0, 128), mt_rand(0, 128), mt_rand(0, 128));
    }
}
\alvin0319\SimpleMapRenderer\util\ImageUtil::toPNG($filePath, $colors);