If a user logs into your course and they see the "Page Not Found" system page, it means the page they are trying to access does not exist.
It's a smart idea to redirect your users to another page with a button or a message placed on the page itself, as shown below:
Redirect a Deleted Page
When you delete a page and it does not exist anymore, a smart thing to do would be to redirect the URL of this page to a new URL or another link which might be more relevant.
To redirect a page, open your Website Settings > URL Redirects > Add New Redirect
Old URL: the URL details of the deleted page
New URL: the new URL path. If your new path is a new link, you can add the entire link as shown below.
Redirect Type: Permanent or Temporary. Permanent redirects preserve the SEO value of the previous page.