For the FAQ topic the site setting name is guidelines_topic_id
I found it in this post: How to fix faq, privacy policy and tos page? - #3 by rieko.
It might be best to first check to see if the old TOS, Privacy, and FAQ topics exist. You could do that by checking the value of each of these site settings from the Rails console, then checking to see if you can find the deleted topics via the UI:
tos_topic_idprivacy_topic_idguidelines_topic_id
With the ID that is returned from each setting, you can try to find the deleted topic by going to /t/-/<topic_id_from_setting_value>. If the topic exists, it should be possible to undelete it through the user interface. If the topics do not exist, my assumption is that new topics can be created in the Staff category. You will then be able to set those topic ids as the value of each of the settings I listed above. I have not tried doing this myself, but I can test it out on my local dev site if you are unsure about making the change on your site.