I followed the tutorial and failed to find the “submit” section too initially. Later I found this was because I did not paste correct code into the new “product-customizable-template”.
Which means, to correctly follow this:
Delete all of the default code so that the file is empty. Copy all of the content from your product-template.liquid file (in the Sections directory), and paste it into your new product-customizable-template file.
-Delete all the code from “product-customizable-template” (in the Section folder).
-Find the “product-template.liquid” from the Section Folder. Note: this file from Section folder NOT the Template folder we created earlier.
-Find the “submit” keyword, press “Command+F” to find it.
I hope that helps.