The code of the book needs to be edited. If you have no idea how to do that yourself, then find someone who can. Without editing it's very hard to create a decent layout beyond anything but the most basic level, and you'll get irate readers complaining about your formatting. Poorly formatted books are not acceptable these days even if self-published.
You may find some tips in this thread:
https://www.mobileread.com/forums//s...d.php?t=295102
and in other threads in the workshop subforum:
https://www.mobileread.com/forums//f...play.php?f=178