BundleBuilder is installed automatically when you install the app. You can check on the status of the install by clicking on "Settings" and looking at the "Installation" section.
Bundle Builder installation screen
The installation process will install a single snippet in your current theme, in the "Snippets" section. The file ensures customers are automatically navigated to your bundle page.
If you are using a new theme, or have deleted the snippet, you can reinstall by clicking 'Reinstall' here.