My iphone 7 not showing ios 14 update

If you are using iOS beta, then you will have to report issues with beta with the feedback app that is downloaded with the profile. If you wish to go back to the public version of the iOS, see this, How to uninstall iOS beta software - Apple Support

Take a look at this user tip:--> Updating iOS: common issues and solutions - Apple Community

Regards

Giulio

Have you ever used beta profile? Are you connected to wi-fi when you are checking for this update, or are you using the computer and iTunes?