my phone software is not updated latest version

Hello~ Your iPhone 7 can’t be up any fu than iOS 15. You need a newer iPhone. Click on below…

iPhone - Apple Official Site

If you purchase a second hand device please take a moment to read these helpful links by clicking on below to make an informed decision…

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~

US_82 wrote:

I have older version ios15.8.3

As Katana-San explained, your phone CANNOT be updated to the latest version. It is as updated as it can be.

An iPhone 7 can not run anything later than 15.8.3.