Well, if you have accidentally purchased a particular book or if in case you do not like a book after buying it, you can return it back to Kindle, and you also will get a refund for that book. But make sure that you request a return within a period of 7 days from the date of purchase of the Kindle book. If your refund is issued, then, in that case, you can no longer access that book.
Now, to return the Kindle book:
First click here, to go to Manage Your Content and Devices.
Then choose the Actions button that is located next to the book that has to be returned.
Then click or tap on the Return for Refund.
You will get a pop-up window. Here select the Return for Refund.
If in case your book was purchased by accident, you can prevent such things from happening again by parental control measures on Kindle. This restricts access to the Kindle Store, Amazon Appstore, and many more places.