AWS EC2 and Elastic Beanstalk

I am new to AWS and the question may seem very basic. However I need to see if I can find a solution to this. I have created and launched an EC2 instance first and then created an ELB instance with a sample application deployed on it. By default, the ELB attaches "Default Environment" to this instance and I find no way to change this to my EC2 instance. How can I attach my EC2 instance (that I created earlier) to this ELB instance? I am using Amazon Free Tier to learn.

Thanks a lot for your time and patience.