I am using the child theme and want to make changes on a few php files, I don’t see the files in the child theme. If I make the changes in the main theme , will I loose them on updating? If so how can I doit without loosing my changes?
Your request is not possible I am afraid as when it comes to wordpress child theme + php changes, what you wish to change reflects on how the php fiels modified in child theme. It’s part of the change you decide to make.
We could only add what is needed to activate a child theme and in style.css you can do simple css overrides from there.
But for more changes you need to know WordPress development in child theme. I know it’s not the answer you wish, but it’s the only possible way.