Sorry, I haven't done that before.
If I try to create a pull request, I get the compare changes page. But on this page I cannot select my repository though I have created it by clone Nim/devel.
Thanks for a help hand, Helmut
In order to create a PR for Nim you need to fork it, it is not enough to clone and modify it.
You can follow this guide: https://www.freecodecamp.org/news/how-to-make-your-first-pull-request-on-github-3/
Steps are: