With the value "index=numbered" within the document class "scrbook" I changed the chapter head in this example from "MyIndex" to "2 MyIndex". In the pagehead
How does LaTeX typeset headers and footers? - Overleaf, Online
Headers and footers - Overleaf, Online-LaTeX-Editor
header footer - Per-chapter page numbers ( GitHub - Wandmalfarbe/pandoc-latex-template: A pandoc LaTeX tikz pgf - Headers and page numbers in external borders - TeX Beamer - Is It Possible To Get Rid of The Bullets in The Page numbering in header/footer (fancyhdr) - TeX - LaTeX Stack Page numbers and headers - TeX - LaTeX Stack Exchange Latex, PDF, Te X table of contents - Headers for specific pages of the document and Page Formatting