Custom navigation in custom post type?

Hi everyone,
I’m working on a site that is basically a single page site, but with product details. Each product that is shown in the portfolio is a custom post type. When you click on the item, the site redirects you to a new page. I would like to replace the main navigation on that type of pages with a simple “back” button. I’m fairly new to WP and Sydney, so maybe someone can help me?
Thanks