App/Themes/Transitions.js

import {Navigator} from 'react-native';

// Transitions could be any of those provided by SceneConfigs
// https://github.com/facebook/react-native/blob/master/Libraries/CustomComponents/Navigator/NavigatorSceneConfigs.js
// OR
// Something custom that you've created.

const transitions = {
  default: {
    ...Navigator.SceneConfigs.HorizontalSwipeJump,
    gestures: null
  },
  modal: {
    ...Navigator.SceneConfigs.FloatFromBottom
  }
};

export default transitions;