update my phone to ios16

And if the app requires iOS 16 you cannot download the app. Your phone is too old and there NO WAY to download iOS 16 to it. I already provided the solution above, which is if you need this app, then you have to buy a newer iPhone.

Sorry, but that is not possible on iPhone 6s. It lacks the hardware required to run iOS 16. If you need it for an app, then it's time to invest in a newer, more modern iPhone.