Step 1: Click on the Objects tab of the S3 bucket.

Step 2: Click on the Upload button.

Step 3: Drag and drop all files and folder build folder to the S3 console.

Step 4: Click on the Upload button on the S3 console.

Step 6: Open website endpoint (Which we save in Step 10 of Setup AWS S3) in the browser.

https://www.cloudthat.com/resources/blog/step-by-step-guide-to-deploy-reactjs-app-on-aws-s3/