I want iOS 16.7

iPhone 6s, iOS 15

If it is an iPhone 6S you can updateyour iPhone to iOS 15.7.9, you can check by reading this Apple article: iPhone models compatible with iOS 12 -> iOS 16.

iPhone models compatible with iOS 15.5 – Apple Support (UK)

iOS 15.7.9 is the latest iOS security update for iPhone 6S.

👉 iPhone 6S can’t be update to a higher iOS (16 and later). 

You cannot pick and choose an iOS version. What you get is Settings > General > Software update > [All options are available here]

You need to correctly Identify your iPhone model - Apple Support

These are the iOS options based on an iPhone Model -->

• iOS 16.7
  • Chipset A11 - 8 (2GB RAM) / 8 Plus (3GB RAM) / X (3GB RAM)

Know how to...

• Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
• Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)