Walkie-talkie dose not appear on my Apple Watch

Hello.

Make sure that FaceTime is installed and activated on your iPhone. Restart Apple Watch.

If you still don't see the Walkie-Talkie app and you're using watchOS 5, contact Apple Support.

Which country you in? As it does not work in all countries

It is currently available in Saudi Arabia. This might help you....https://support.apple.com/en-us/HT208917