You have to choose one of two options here:
This is a public domain work.
This is not a public domain work and I hold the necessary publishing rights.
If you wrote the book, the book is not a public domain work, and you do indeed have the necessary publishing rights. Amazon says the following in the information in the “(What’s this?)” link:
Publishing rights are the rights you need to publish a book. To publish a book for Kindle through KDP, you must have obtained all rights necessary to publish the digital book from the book’s author and any other content creators, or, if you are the book’s author, you must have retained all of the necessary digital book publishing rights.
And then Amazon has this to say about public domain material:
If you are publishing a public domain book, keep in mind that the duration of copyright varies between countries, so ensure that you indicate your territory rights accurately. (If your book is in the public domain in one country but not another, you must identify your territory rights accordingly.) Books that consist entirely or primarily of public domain content are not eligible for the 70% royalty option.
Amazon’s Publishing Public Domain Content page has further guidelines regarding when you can publish public domain content. In short, you need to differentiate what you’re publishing from similar existing public domain content in the Kindle store. You can do this in three ways:
If you create a new translation of public domain content from another language, you can publish it as a new translation. If you annotate a public domain work with additional insight, critique, biography, historical context, or other information, you can publish it. And if you provide at least ten or more unique illustrations to go along with the content of the book, you can publish it.