If you’ve already installed the themes inside WordPress there is no need to do this.
- Extract the react.zip and react-child.zip files, you will end up with two folders named react and react-child
- Inside your FTP software, connect to your server and browse to the wp-content/themes/ directory
- Upload the react and react-child folders into this directory
- Inside WordPress go to Appearance → Themes
- In the list of themes you should now see React and React Child, hover over the React Child theme and click Activate