Login to your AWS Account
Go to your EC2 Panel and select your region
Select Load Balancer from left navigation menu
Found Load Balancer which related to your Beanstalk App
In Description Tab grab Hosted Zone ID
Open Route53 Panel
Select your domain hosted zone
Add A Record for .YOUR-DOMAIN.com
Select Alias option to Yes
Search for your Load Balancer related to you app
Confirm it's Hosted Zone ID with what you grabbed in step 5
Do steps 8-11 for www.YOUR-DOMAIN.com as well.