Firstly, in your react project go to your package.json file and adjust this line of code to match your destination domain address + folder:
"homepage": "https://yourwebsite.com/your_folder_name/",
Secondly, go to terminal in your react project and type:
npm run build
Now, take all files from that newly created build folder and upload them into
your_folder_name, with filezilla in subfolder like this:
public_html/your_folder_name
Check in the browser!