Remove rhombus question marks from newly created epub

I created an ebook (epub) from a Project Gutenberg book that was in html format after importing it into calibre but the result has rhombus question marks. Otherwise it came out pretty good. How do I remove these rhombus marks from the newly created epub? If I have to redo it that's okay but I just want an epub free of these marks.

https://i.imgur.com/EafI07i.jpg