Modifying back button with react-navigation on specific screen

Consider, that you have 3 screens A, B, C respectively. So, the default functionality of the back button in StackNavigator is:- If you press the Back Button on screen C, it will take you to the previous screen i.e, screen B. To override that you could do something like this on screen C:-

import { HeaderBackButton } from 'react-navigation';
static navigationOptions = ({navigation}) => {
  return{
    headerLeft:(<HeaderBackButton onPress={()=>{navigation.navigate('A')}}/>)
 }
}

You can override back button for a specific screen with navigationOptions of that screen. You can read more info about overriding back button in react-navigation docs

Example from docs

class HomeScreen extends React.Component {
  static navigationOptions = {
    headerTitle: <LogoTitle />,
    headerRight: (
      <Button
        onPress={() => alert('This is a button!')}
        title="Info"
        color="#fff"
      />
    ),
  };
}

Overriding the back button

The back button will be rendered automatically in a StackNavigator whenever it is possible for the user to go back from their current screen — in other words, the back button will be rendered whenever there is more than one screen in the stack.

Generally, this is what you want. But it's possible that in some circumstances that you want to customize the back button more than you can through the options mentioned above, in which case you can specify a headerLeft, just as we did with headerRight, and completely override the back button.