Child theme – copied some files from parent to child website still uses parent files

Try to override the parent theme functions instead of creating your child theme header-functions.php file. Here is a reference on how it can be done : https://www.mhthemes.com/support/overriding-parent-theme-functions-child-theme-tutorial/

Check if the parent theme header-functions.php file is implementing pluggable functions. Then you can override them in your functions.php file.