Q: Iphone 6s front camera is not working

Sorry, but if setting it back to factory settings without using any backup data did not bring back the front camera function, you'll have to get the phone serviced, your device is still under warranty.

If you are outside of the country of purchase, you'll have to bring it back to that country, the warranty for an iPhone is only valid in the country of purchase and Apple does not ship internationally.

Start a service request

Find an Apple Authorized Service Provider

Make an Apple Store appointment

Yes, that's one one the downsides of buying abroad. But if you have a person you can trust, that is traveling to or living inside that country, you could let them take care of that.