Unfortunately, there is no setting in the Divi Contact Form Module to add attachments of upload files. This is a popular Divi feature request, but there is currently no information on if or when this will be implemented.
There are many good contact form plugins available for Divi. Some are free within the WordPress repository, such as Caldera Forms, Contact Form 7, and Ninja Forms.
There is one great Divi Contact form alternative that adds the ability to add attachments and files. This plugin, which is made specifically for Divi, is called the KK Custom Form and is sold by Elegant Marketplace.