How to add Kirby 3 file template to Kirby 2 images

index.php

<?php

require __DIR__ . '/kirby/bootstrap.php';

// echo (new Kirby)->render();

$items = page('blog')->children();

foreach ($items as $item) {
    if ($i = $item->cover()->toFile()) {
        $i->update([
            'template' => 'cover',
        ]);
    }

    foreach ($item->gallery()->split(',') as $image) {
        if ($i = $item->file($image)) {
            $i->update([
                'template' => 'gallery',
            ]);
        }
    }

    $item->update([
        'cover' => null,
        'gallery' => null,
    ]);
}