Uninstall, install a theme: 

export theme_name='THEME_NAME'
drush theme:uninstall $theme_name

drush config:set system.theme default $theme_name -y

Run some code with drush:

php -d memory_limit=512M ./vendor/bin/drush -l wco.local php:eval '
  $config = \Drupal::configFactory()->getEditable("core.extension");
  $themes = $config->get("theme") ?: [];
  unset($themes["ish_drupal_theme"]);
  unset($themes["wco_drupal_theme"]);
  $config->set("theme", $themes)->save();
';

.