Hi Vishal,
Welcome to Open Astronomy! You are free to contribute to any open source
project, don't need to wait for a person to give you permission (that's
the beauty of open source 😉).
First you need to find the sub-organisation that attracts you the most -
either because the topic or the technology they use. Then visit their
issue tracker and look for the "good-first-issue" label. If you don't
find any, join their chatting platform and ask whether someone knows of
a good issue to start with.
Try to fix it, ask for help when you get stuck and open a pull-request
early (now you can mark them as draft if it's not finished), ask for
comments and review. When it's done you get another issue of their list,
and repeat.
Good luck!
David