You're using the regular iPhone Messgaes app? If so, then when viewing all of your conversations, you should have an "Edit" button you can press on the top-left, and can then select which conversations to delete. or, for individual messages, you should be able to press and hold on the message to delete it.
If that isn't working for you, then what part of it fails?
Hi . Elements , i know what you mean , you are right , if the author want to delete messages form their iPhone , he can manually delete them on the iPhone, but you you're missing a point , any data on the phone is hard to be deleted completely,they're just being erased from the phone surface , they will be found on iPhone with some ways ,
I went back to the company and asked my colleague how to delete messages from iPhone ?
The most popular answer is to delete manually , they may not be immediately removed from the phone , if you want to delete them immediately ,you can read the above course, let me know whether you succeed or not