I am not able to recover deleted messages on my iPhone

No way to do that. No backup = No recovery, sorry.

The support article that led you here is valid only for iPhone models running iOS 16 or later, and releted to messages you delete using that iOS version.

Regards

Giulio

That is a feature of ios 15. It will not be available on your iPhone 7.

You should run iOS 16 or later (unfortunately not possible on an iPhone 7 or 7+)