How to update iOS on my iPhone?

iPhone 6s can be updated to iOS 15.x (but not 16.0 or later). Please do so. How to update your iPhone - Apple Support

Each app has its own system requirements, as determined by their developers. Some apps for iPhone may have system requirements of iOS 14.x, or 15.x, or later. You wouldn't be able to run those apps on iOS 13.x. Older versions of apps may become unsupported for their initial services, so that is generally not a valid workaround. Older versions of apps may not even be available anymore through the App Store.

The Uber app requires iOS 15 or later.

The Lyft app requires iOS 15 or later.

iOS 15 requires iPhone 6s/6s Plus/SE (1st gen)/7/7 Plus. iPhone 6 or earlier are not supporting iOS 15.

Update iOS on your iPhone or iPad - Apple Support

I used to do Uber and lift they ask me to update my Apps I can’t

Please help me

With what?