Why can't I find FaceTime on my iPhone 8?

See if the first paragraph applies.

FaceTime - Find or restore a missing app

nathish wrote:

i bought this from dubai and my version is 12.4

In which case the first paragraph in the link provided by Eric does Apply. Did you even read the first paragraph?

Make sure that your device supports FaceTime. FaceTime isn’t available or might not appear on some iPhones and iPads purchased or used in Saudi Arabia, Pakistan, and United Arab Emirates, including Dubai.

Dubai is part of the United Arab Emirates where Facetime is outright banned. That iPhone can never have Facetime unless its using one of the allowed carriers in the Middle east.

If you are using the iPhone in Pakistan or Saud Arabia, Facetime might be available.

Are you using the iPhone in one of those countries with a carrier there?

If not, Facetime is still not going to be available.

Where was the phone purchased?

See the download section of this article.

Apps - Remove built-in Apple apps from the Home screen on your iOS device or Apple Watch

Where, what country, did you buy this iPhone?

What model number does it have in Settings->General->About->Model?