I have asked this question on reddit afterwards.
https://www.reddit.com/r/zsh/comments/jcju5h/extend_git_completion_function/

I got a solution from there. However, I am always looking for betterment.

*Thanks and Best Regards,Ahmad Ismail*


On Sat, Oct 17, 2020 at 9:24 PM Bart Schaefer <schaefer@brasslantern.com>
wrote:

> On Sat, Oct 17, 2020 at 1:33 AM Oliver Kiddle <opk@zsh.org> wrote:
> >
> > In this case, it's probably easier to tweak the original _git-diff
> > function than to modify it from a wrapper.
>
> I was thinking there should be some way to implement this with a
> zstyle by changing the program invoked by _call_program for the
> "files" style, but I didn't have time to work out the incantation for
> doing that in the nested subcommand context.
>