Old way - use .ebextensions/*.config in AWS CLI and modify the file that has environment variables . Or you can add, edit and remove environment variables in the Elastic Beanstalk web interface.
The variables are under Configuration → Software Configuration:
![Environment Properties](https://lh5.googleusercontent.com/1Sv_dsnVkARwuoBQ5siCYxcaiJ8irkCowdmn62Qq2irul4Rph0ft_x7Rcbm_bOpZu_tfgywxJDSlRRmgWqPhM5DMqjmfBv6cIbUwaE49-COG39C7wjoJe6AdyzoNjKhD1Zc9D5NW)