You can find the Writing Mode page for your book by going here:
https://leanpub.com/YOUR_BOOK/settings/writing_mode
...making sure to replace YOUR_BOOK with your book's unique web address.
You can also find this page on your Book's Overview page:

You can find the Writing Mode page for your book by going here:
https://leanpub.com/YOUR_BOOK/settings/writing_mode
...making sure to replace YOUR_BOOK with your book's unique web address.
You can also find this page on your Book's Overview page: