I want my iPhone 7 to be updated

An iPhone 7's CPU isn't capable of 16 or above; this isn't upgradable. To install 15.7.3, use a computer or the Software Update function in Settings.

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Not possible to update the iPhone 7 to iOS 16, if that is what you are asking.

Best that the iPhone 7 can do is iOS 15.7.3

Settings > General > Software Update