Good question.
I have no “Guidelines” in the About page, but let’s assume you meant FAQ. 
I don’t know any fast way to recover a deleted topic as they don’t appear in topic lists, as opposed to posts.
But they are auto-generated when a new Discourse instance is created. They may share the same ID on every Discourse instance unless the FAQ URL was manually changed.
Try opening https://yourforum.com/t/5 and see if it opens the deleted FAQ topic.
If you want to link FAQ to a new, arbitrary URL, you can look for the faq url site setting