unable to see FaceTime App, cannot download it, Dubai bought iphone- now using in India

You can use FaceTime over Wi-Fi1 or over cellular on supported iOS or iPadOS devices2. FaceTime isn’t available or might not appear on devices purchased or used in Saudi Arabia, United Arab Emirates, and Pakistan. 

However, with iOS 11.3 and later, FaceTime is available on iPhone, iPad, and iPod touch in Saudi Arabia. And with iOS 12.4 or later, FaceTime is available on iPhone, iPad, and iPod touch in Pakistan. Update your device to get FaceTime in Saudi Arabia and Pakistan.

Use FaceTime with your iPhone, iPad, or iPod touch - Apple ...

shinija wrote:

I got an iphone from Dubai, UAE (iPhone 7) iOS 12.4.1

I started using it in India- I am in India now .

How do I start using FaceTime in India now .

As stated above: you can not use FaceTime on that phone in India. You need a model from a region where FaceTime is not banned or restricted.

That model will not have FaceTime in India. That restriction can not be overcome.