Putting timestamp in CHANGELOG.org of modus-themes

[fatiparty--- via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

Nov 7, 2021, 18:25 by help-gnu-emacs@gnu.org:

> irenezerafa via Users list for the GNU Emacs text editor wrote:
>
>> Am using modus-themes for emacs, and at the end of
>> modus-themes.el, there is the following code
>>
>> (provide 'modus-themes)
>>
>> ;; Local Variables:
>> ;; time-stamp-pattern: "Last-Modified: <%Y-%02m-%02d %02H:%02M:%02S %5z>"
>> ;; End:
>>
>> ;;; modus-themes.el ends here
>>
>> To insert the timestamp, I put (add-hook 'before-save-hook
>> #'time-stamp) in the emacs init file,
>>
>> But I also need a way to synchronise the timestamp from modus-themes.el into the
>> CHANGELOG.org. What can I do for the time stamp to be inserted.
>>
>> I would like to have after the line
>>
>> #+OPTIONS: ':nil toc:nil num:nil author:nil email:nil
>>
>> the following
>>
>> Copyright (C) 2019-2021 Free Software Foundation, Inc.
>> Author: Protesilaos Stavrou <info@protesilaos.com
>> URL: https://gitlab.com/protesilaos/modus-themes
>> Version: 1.6.0
>> Last-Modified: <2021-11-05 10:36:21 +0200
>> Package-Requires: ((emacs "27.1"))
>> Keywords: faces, theme, accessibility
>>
>
> Open the file in a buffer from Lisp, search for that line,
> format your data, insert it into the buffer, save/write the
> buffer to the file. Try to do each step interactively, when
> all of it works put it together into one function and have the
> hook call it.
>

Can you give me a small elisp example to help me?