To display product designer editor please follow the steps
# Please create a page first with shortcode on content
# Then go to Product Designer >Add Templates Create a template first. add your template sides image and select options.
# Then go to product edit tabs see Product Designer tab and select created template.
# For variable product you will see the options under variations
# Then go to Product Designer > Settings page and set the option Designer page select the page you just created.
N.T, this is not necessary for latest version, the designer will load it on the product page. once you click on customize button.
You are almost done, when you are visited WooCommerce shop page or single product page you will see the customize button.