ReactJS: Getting Failed to Compile Error While Starting the Server - reactjs

Question

I am a beginner in ReactJS. Just after finishing a course on the basics of React and Redux. I have started a new Udemy course entitled "React Data Visualization - Build a Cryptocurrency Dashboard." I am facing a problem in lecture 4 while trying to start the server with yarn start command:
Failed to compile
./src/index.js
Cannot find file: 'index.js' does not match the corresponding name on disk: '.\src\App\app'.
Here are my codes on index.js file under app directory:
import React, { Component } from 'react';
import './App.css';
class App extends Component {
render(){
return (
<div>
Hello World
</div>
);
}
}
export default App;
Here are my codes on index.js file under src directory:
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
ReactDOM.render(<App />, document.getElementById('root'));
// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
How can I fix the issue?
You can find the project files here.
https://drive.google.com/open?id=1u-8mCYSWZtXPbIqELKsF33FOiXb3yrkH
Edit 1: I am adding the codes inside package.json file, as suggested by #Wesgur:
{
"name": "cryptodash",
"version": "0.1.0",
"private": true,
"dependencies": {
"#testing-library/jest-dom": "^4.2.4",
"#testing-library/react": "^9.3.2",
"#testing-library/user-event": "^7.1.2",
"react": "^16.12.0",
"react-dom": "^16.12.0",
"react-scripts": "3.4.0"
},
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test",
"eject": "react-scripts eject"
},
"eslintConfig": {
"extends": "react-app"
},
"browserslist": {
"production": [
">0.2%",
"not dead",
"not op_mini all"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
]
}
}
Edit 2: I am adding the image to show the folder structure, as suggested by #Madhavan.V:

Answer 1

#Shawan It is just a typo change the App import statement in src/index from import App from './App'; to import App from './app';.

Answer 2

import App from './app';
this will import your index.js of app folder.