WP + MySql db / PHP

Following on from Scott and Milo’s answers, you should take a look in the theme directory. If you browse the website file directory: /wp-content/themes/generatepress/
Look for a filename like page-template-signup.php

That said, since GeneratePress is a premium theme, you need to keep in mind if you make changes to that file, you will lose them when you update the theme.

The standard WordPress way around this problem is to use a child theme, which you can Google to find out more.

tech