Add the following code to your functions.php file. Replace the array with the correct templates for your site.

  array('slug' => 'home', 'label' => 'Home'),
  array('slug' => 'about', 'label' => 'About'),
  array('slug' => 'contact', 'label' => 'Contact')

Add the rest of the code to your functions.php file.

 * Add file-less page templates to the page template dropdown 
add_filter('theme_page_templates', function($page_templates, $wp_theme, $post) {
  foreach(CUSTOM_PAGE_TEMPLATES as $template) {
    // Append if it doesn't already exists
    if (!isset($page_templates[$template['slug']])) {
      $page_templates[$template['slug']] = $template['label'];
  return $page_templates;
}, PHP_INT_MAX, 3);

The templates will now be selectable in the Page Attributes.

Page Attributes - Template