AWS Elastic Beanstalk .ebextensions Setup

I need someone who is experienced with AWS Elastic Beanstalk to configure a file in .ebextensions to make it so that the nginx.conf is edited to set "client_max_body_size" to 50 megabytes. Currently, when a new EC2 instance is deployed, it disables the previous instance. The new instance will not have the same changes to the config file, breaking the service.