When you make a product customizable on Zakeke, on the product page you will see by default only the "Add to cart" button: clicking on it, the customer will first go through the customizer.
If you wish to show a "Customize" button as a dedicated call-to-action to initialize the customizer, please follow these steps:
Go to your PrestaShop admin panel > Modules > Modules Manager > Zakeke > Configure > Force Product Customization > No
Once saved, you'll see the "Customize" button on the product page.