Hi MoonCusser,
To navigate to public-facing website edit page, please perform the following steps to check if any errors.
1. Access the website in your browser, and then click Member Login on the home page.
2. Then click these buttons in order: Website->Web Pages->Pages->Edit->Setup.
To see the details about these steps, this article for your reference. Modify the page setup and display options for a public-facing website
In addition, if you would like to get more description about customizing the public-facing website, this online article is recommended: Customize the public-facing Website. Based on my experience, for SharePoint Online tutorial and instructions, you can search the key words on Office.com and TechNet. If you have any questions when using Office 365, it's always our pleasure to be of assistance.
Thanks,
Maggie Li