My safari browser is automatically vanished I don't know how, this is not available in AppStore . How can I download it???

There is an old old old d thread saying about your problem, My safari browser has disappeared And here I copy the solution from randers4.

"Check Settings>General>Restrictions, make sure Safari is set to On. If it is, then look on all your screens and inside all your folders as Sarari can't be deleted. If you still can't find it go to Settings>General>Reset>Reset Home Screen Layout. This will restore the home screen to its original configuration but may move other apps around to do so."

I don't know whether it can actually fix your problem but I hope it can.

Restoring your iPhone will restore iOS, which includes Safari (assuming your iPhone is not jailbroken).

Restore your iPhone, iPad, or iPod to factory settings - Apple Support