To display product designer editor please follow the steps
# Please create a page first with shortcode on content
# Then go to Product Designer > Templates Create a template first.
# 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.
You are almost done, when you are visited WooCommerce shop page you will see the customize button.