The Posting Team, who post the books, also make the corrections, and ultimately, the corrections need to go to them.
Many producers put their e-mail addresses in their texts, specifically so that readers can contact them when errors are found. If you see that in your text, you should try to contact the producer first. This is especially true if the corrections aren't obvious, as in the case of missing words. The producer is likely to have the original book, and will probably be able to confirm your corrections without visiting a library. If the book needs the corrections, the producer can then notify the Posting Team.
If you get no response from the producer, or if there is no e-mail address listed, or if the corrections are small and obvious, you should send them to the email address for reporting errors listed on the Contacts Page where members of the posting team will deal with them.