I want to reset my restriction password cos I forget the old password I can't recall at all

You would need to restore as new to get rid of the old one. From there you can set whatever you like.

The above comes from this article:

Use Restrictions on your iPhone, iPad, and iPod touch - Apple Support

It certainly makes sense that naturally, if you don't recall the restrictions password you cannot simply reset it. If you could, anyone could simply undo an existing password.