Can I insert RN code in my existing native app?

Below things is my situations(, needs)

1. I have existing native app(Android and IOS).
2. I wanna add a new function to my native app.
3. the new function should be made using React Native code (because of code reusing)

So, Can I call RN code in my existing native app?if it can do, HOW????and Is it not good idea(or way)??