Re: i purchased iphone 6 from dubai and no facetime how i can install it
Welcome to iMore! FaceTime is a stock iOS app and can't be downloaded separately. What you might want to try is restoring your iPhone using iTunes and setting it up as new. Here's a detailed how-to article: https://support.apple.com/en-us/HT201252. Just make sure that you're signed into iTunes on a Mac/PC using a US-based iTunes account.
Basically it boils down to this: you can't. Facetime (as well as other VOIP services) is banned in the UAE and there is no way to install it on an iPhone that was manufactured specifically for that market. Apple was forced by law to make sure phones made for the UAE would never ever be able to run Facetime if they ever wanted to enter that market so they did.