First, air out the book by turning on the fan a few times, then expose the book to the sun for a while. Second, if they still smell, sprinkle baking soda on the pages and let it stay on them for a few days. Third, if you still smell mold on them, put the books in a zippered but unclosed plastic bag and place in the freezer to kill the mildew. Repeat with the remaining books.
https://www.washingtonpost.com/lifestyle/advice/hints-from-heloise-keep-valuables-safe-holiday-traveling/2021/12/02/e98d4e5c-5252-11ec-9267-17ae3bde2f26_story.html?utm_source=rss&utm_medium=referral&utm_campaign=wp_lifestyle Hint from Heloise: Keep your valuables safe while traveling during the holidays