If the issue persists, let's try navigating your QBO account using a private browser to rule out the possibility of a webpage issue. To save you time, use either of these keyboard shortcuts:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari: Command + Shift +N
Once done, revisit the link again. If you're able to see the training page using a private browser, go back to your regular browser and clear its cache. Clearing the cache or cookies is the best way to get a clean slate for your browser. Otherwise, using other supported browsers can be a good alternative too.
Here are some articles that you can check out about exam guide and certification FAQs for your reference: