ios 16 help iPhone 7

Hello ~ Your iPhone 7 cannot be updated to iOS 16 you need a newer device. Should you select a second hand device (iPhone 8 or up) please take a moment to read these…

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

The iPhone 7 can be updated to iOS 15.7, no further.

See the article(s) below. 

iOS 16 compatible devices