This is a beginner's question, but somehow I couldn't find the answer.
I would like to colloborate on a repo and submit my contribution (this is my first contribution).
I would like to commit from my private account while crediting the commerical company I work for, which is not listed as an organisation in GitHub.
How can I credit my company?
That's an interesting question. I don't think that there is a built-in process for this since contributions usually go to people and not organizations, but there's nothing stopping you from crediting the company that you work for in your commit messages. What form of credit are you looking to offer to your company?