Override form.html.twig into module
You need to alter the Theme registry and set the path of the hook suggestion "form" to your_module/template path as bellow: 

/**
 * Implements hook_theme_registry_alter().
 */
function My_Module_theme_registry_alter(&amp;$theme_registry) {
  // You can add some conditions here in case you want
  // to override the form template only for some reasons.
  $theme_registry['form']['path'] = drupal_get_path('module', 'My_Module') . '/templates';
}


And the structure of your module should be: 

-- My_Module
  +-- templates
     +-- form--pom-mapping-setting-form.html.twig