Use DeleteBucketCors with an AWS SDK or CLI

        /// <summary>
        /// Deletes a CORS configuration from an Amazon S3 bucket.
        /// </summary>
        /// <param name="client">The initialized Amazon S3 client object used
        /// to delete the CORS configuration from the bucket.</param>
        private static async Task DeleteCORSConfigurationAsync(AmazonS3Client client)
        {
            DeleteCORSConfigurationRequest request = new DeleteCORSConfigurationRequest()
            {
                BucketName = BucketName,
            };
            await client.DeleteCORSConfigurationAsync(request);
        }

The following command deletes a Cross-Origin Resource Sharing configuration from a bucket named amzn-s3-demo-bucket:

aws s3api delete-bucket-cors --bucket amzn-s3-demo-bucket

class BucketWrapper:
    """Encapsulates S3 bucket actions."""

    def __init__(self, bucket):
        """
        :param bucket: A Boto3 Bucket resource. This is a high-level resource in Boto3
                       that wraps bucket actions in a class-like structure.
        """
        self.bucket = bucket
        self.name = bucket.name


    def delete_cors(self):
        """
        Delete the CORS rules from the bucket.

        :param bucket_name: The name of the bucket to update.
        """
        try:
            self.bucket.Cors().delete()
            logger.info("Deleted CORS from bucket '%s'.", self.bucket.name)
        except ClientError:
            logger.exception("Couldn't delete CORS from bucket '%s'.", self.bucket.name)
            raise

require 'aws-sdk-s3'

# Wraps Amazon S3 bucket CORS configuration.
class BucketCorsWrapper
  attr_reader :bucket_cors

  # @param bucket_cors [Aws::S3::BucketCors] A bucket CORS object configured with an existing bucket.
  def initialize(bucket_cors)
    @bucket_cors = bucket_cors
  end

  # Deletes the CORS configuration of a bucket.
  #
  # @return [Boolean] True if the CORS rules were deleted; otherwise, false.
  def delete_cors
    @bucket_cors.delete
    true
  rescue Aws::Errors::ServiceError => e
    puts "Couldn't delete CORS rules for #{@bucket_cors.bucket.name}. Here's why: #{e.message}"
    false
  end

end