Programmatically add template to images

config.php

<?php

return [
    'routes' => [
        [
            'pattern' => 'imagetemplates',
            'action'  => function () {
                $result = '';
                foreach(site()->index() as $page) {
                    $result .= '<h2>' . $page->title() . '</h2>';
                    foreach($page->files() as $file) {
                        try {
                            $file->update([
                                'template' => 'default',
                            ]);
                            $result .= '<h3>' . $file->filename() . ' ✅</h3>';
                        }
                        catch(Exception $e) {
                            $result .= '<h3>' . $file->filename() . ' ❎</h3>';
                        }
                    }
                }
                return $result;
            }
        ]
    ]
];