How to modify the header? (\chapter*{}, title or just hide the chapter)

[moshpirit]

I'd like to show the title of the chapter, which is fine, but sometimes I use \chapter*{}, so it appears "General index" or the name of a previous section, which is very awkward sometimes. I'd like to be able to modify it so it shows the chapters when they are hidden with * or at least hide this part of the header or show the title of the document instead.

[syvshc]

Could you please upload some pictures to clarify your problem? I didn't understand it.

[moshpirit]

Sure, I mean this:

When I use \chapter*{} and \section*{}, things get messy, and I'd like to be able to modify it so I can show another stuff like the title of the document, the name of the \chapter*{} or \section*{}.

If you want me to share any other kind of information or screenshots, feel free to ask :)

[syvshc]

I think that this question has nothing to do with elegantbook. In book class things work the same.

% \documentclass{elegantbook}
\documentclass{book}
\usepackage{fancyhdr}
\usepackage{lipsum}
\begin{document}
  % \maketitle
  \chapter{test chap}
  \section{test sec}
  \lipsum[1-20]
  \chapter*{}
  \section*{}
  \lipsum[1-20]
\end{document}

In \chapter*{}:

[moshpirit]

EDIT: Ok, I think that it kinda has to do with the template because the customization of fancyhdr is there but in the Headers and footers Overleaf's guide there's an explanation on how can it be changed, so I think that's cool with me :)

Thank you so much anyway for responding.