If you use IIS you can have:

1. One site for example:"MyWebsite"
2. Add resource build of react in main path of "MyWebsite"
3. right click on website name and add application in "MyWebsite" and name for example "api", you need /api for yor base url in react calling api or use url rewrite
4. Start application

Now you have one website on iis working with 1 port for your both application