how to download IOS16

You cannot get iOS 16. It hasn't been signed for at least 2 years now. You can only update to the most current version available for your device. For iPhone 11, that means you can update to iOS 17.7 or you can update to iOS 18, the newest iOS version.

See this link if you can't update your iPhone for possible solutions --> If your iPhone or iPad won't update - Apple Support (QA)

My iPhone has been offering me a choice of updates to iOS 17 or 18 – so the OP will probably get a choice of those two. It seems likely that the window to get iOS 17 (if one is not running a version of it already) will not stay open for long.

This is the English speaking community, so I'm afraid I along with most other users can't read Chinese. Can you ask your question more specifically, in English?