I deployed the application for my rails in Deploying the application for rails on AWAS Elastic Beanstalk
1) How can I use reset my database, as in my development environment?
rake db:drop rake db:create rake db:migrate
2) If I create a db migration file, will it automatically start the elastic beanstalk?
You can customize your environment with elastic Beanstalk extensions
http://ruby.awsblog.com/post/Tx2AK2MFX0QHRIO/Deploying-Ruby-Applications-to-AWS-Elastic-Beanstalk-with-Git