My mom never been to flight or airport she need travel to Australia. Now I'm looking for some app where I can find some fellow passengers info and request them to help her so I can book the same flight if I find anyone

I do not know any airline that makes passenger data publicly available so they can be contacted by other passengers whom they do not know.

Anilreddyfzs Welcome FT
That's not going to happen. A random passenger will not help another passenger. Passengers lists are kept very private by airlines.
If she needs help strongly recommend a another family member accompany her. Airlines can offer *very* limited assistance. But passengers must be able to look after themselves.
I note from your profile you are from India.

The best you can hope for is to request passenger assistance via the airline when you book. While you certainly could post the flight info on a social media page, I would caution you not to. This would make her the target of every lunatic there is. It would cause her much more harm. When you book, there will be a place to request assistance. Then after, call the airline to confirm. DO NOT solicit random strangers. Please.

Also, depending on the origin airport, it might be possible for you to escort her past security. A few airports have this available now; however, one way to ensure this is to purchase a refundable ticket to somewhere and take her to the gate. Flight crew are professionals; they deal with people like your mom all the time.