It depends on the complexity of your app and there are two options. I list them in order of preference.
For an app with a lot of connections and to avoid having to re-add any connections, I would export the app and import it in the new environment. This will prompt you and attempt to map the existing connections so you won't have to re-add them. There is a blog post that explains how to do this here -> https://powerapps.microsoft.com/en-us/blog/powerapps-packaging/
For a simple app, with maybe 1-2 connections or no connections at all, you can Open the app first in the Editor, then save the app locally on your PC (not the cloud), switch environment, then Open the app in the editor and re-save on the new environment. You might have to fix the connections you had, by re-adding them as this is not handled as in the first option.
There is a third case if your app is Solution aware, which is similar to the first option.
Hope it helps.
