react-navigation stack headings

app;containers;Signup;containers;EmailPassword.jsx

import React, { Component } from 'react';
import { connect } from 'react-redux';
import Text from 'components/Text';
import { View } from 'react-native';
import { Field, reduxForm } from 'redux-form/immutable';
import { NAV_SCREEN_OPTIONS } from 'constants';
import { FIRST_LAST_NAME } from '../../routes';

export class EmailPassword extends Component {
  static navigationOptions = ({ screenProps }) => ({
    ...NAV_SCREEN_OPTIONS,
    title: 'Create Account',
    headerLeft: <Text style={{ color: '#fff' }} onPress={() => screenProps.parentNav.goBack(screenProps.parentNav.state.key)}>&larr;</Text>
  });

  render() {
    return (
      <View>
      {/*...*/}
      </View>
    );
  }
}

export default EmailPassword;

app;containers;Signup;index.jsx

import React, { Component } from 'react';
import SignupRoutes from './routes';

export class Signup extends Component {
  static navigationOptions = () => ({
    header: null
  });

  render() {
    return (
      <SignupRoutes parentNav={this.props.navigation} />
    );
  }
}

export default Signup;

app;containers;Signup;routes.jsx

import React from 'react';
import { View, Text } from 'react-native';
import { StackNavigator } from 'react-navigation';
import EmailPassword from './containers/EmailPassword';
import FirstLastName from './containers/FirstLastName';

export const EMAIL_PASSWORD = 'EMAIL_PASSWORD';
export const FIRST_LAST_NAME = 'FIRST_LAST_NAME';

const SignupNav = StackNavigator({
  EMAIL_PASSWORD: { screen: EmailPassword },
  FIRST_LAST_NAME: { screen: FirstLastName }
}, {
  initialRouteName: EMAIL_PASSWORD
});

class Signup extends React.Component {
  static navigationOptions = {
    title: 'Signup Screen'
  }

  render() {
    return (
      <View style={{ flex: 1 }}>
        <SignupNav screenProps={{ parentNav: this.props.parentNav }} />
      </View>
    );
  }
}

export default Signup;

app;routes.js

import { StackNavigator } from 'react-navigation';
import LaunchScreen from 'containers/LaunchScreen';
import Login from 'containers/Login';
import Signup from 'containers/Signup';
import { LAUNCH_SCREEN } from 'screens';

const PrimaryNav = StackNavigator({
  LAUNCH_SCREEN: { screen: LaunchScreen },
  LOGIN: { screen: Login },
  SIGNUP: { screen: Signup }
}, {
  initialRouteName: LAUNCH_SCREEN
});

export default PrimaryNav;

App/routes.js contains the primary application navigation used from the beginning
App/containers/Signup/routes.jsx navigation is to be nested within the primary navigation

Put the nested navigation within a screen accessible to the primary navigation, and set header: null. Pass the primary navigation object down as screenProps and use it in the initialRouteName of the nested navigation