I can't reverse-engineer that process, but I can tell you what I do:
Rather than use Word's save as / export to html, I run the document through word2cleanhtml.com which has a free and rather good service online. Alas, it doesn't give you the html template that you will need, so you will have to do some research on how to open and close an html file, and preferably on incorporating a style sheet.
I then open the html in Sigil, a free and rather good software that has its own forum here. I use that to build an epub, which I upload to the KDP and also to Barnes & Noble and the other epub retailers.
(Not that there's anything wrong with MPC! But I haven't used it for years.)