A native profile cannot be copied from a responsive profile. However, any Nanoflow logic you've created can be reused, and Microflow logic can be copy-pasted into nanoflows where necessary. You will need to create specific native pages for your native navigation profile.
It's worth noting that Mendix recently added the ‘Progressive Web App’ option, which would provide you with an offline-capable app which allows you to use your already existing webpages.