How an Azure Functions app can be copied?

There are a couple of ways you can move the content from one Function App to another. The simplest is to copy the contents of your wwwroot folder to the other environment, which you can do by using Kudu, FTP, etc.

Another way that is often simpler and less error prone is to setup CI/CD so that different branches will trigger deployments to different environments. You can learn more about the continuous deployment options here.