1- Is your customization page defined as homepage?
2- Is your customization page defined as one of woocommerce pages?
3- Does the product you are trying to customize exists and is published in your shop?
4- Are you accessing this page from one of the product designer buttons?
This is your homepage which is what most visitors will see when they first visit your shop.
You can change this text by editing the “Welcome” page via the “Pages” menu in your dashboard.