Using the Amazon unified CLI:

• Create a JSON file containing the attributes you want to modify and save it locally as
  /tmp/ElbLogs.json:
  {
  “AccessLog”: {
  “Enabled”: true,
  114 | P a g e”S3BucketName”: “string”,
  “EmitInterval”: integer,
  “S3BucketPrefix”: “string”
  }
  }
• Update the Load Balancer attributes:
  aws elb modify-load-balancer-attributes –load-balancer-name <elb_name> –load-
  balancer-attributes file:///tmp/ElbLogs.json

References:

1. https://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/enable-access-logs.html
2. http://docs.aws.amazon.com/cli/latest/reference/elb/describe-load-balancers.html
3. http://docs.aws.amazon.com/cli/latest/reference/elb/describe-load-balancer-attributes.html
4. http://docs.aws.amazon.com/cli/latest/reference/elb/describe-tags.html
5. http://docs.aws.amazon.com/cli/latest/reference/elb/modify-load-balancer-attributes.html