You can easily uninstall Customized by following these steps:

  1. Restore cart liquid if you used advanced cart install.
  2. Restore product.liquid if you used advanced template install.
  3. Delete page.customize.liquid file.
  4. Delete "Customize" Shopify page.
  5. Remove products in your store that have product type of "Bare Product" or "Custom Product".
  6. Remove App from Shopify App menu.