To copy a Heroku ENV variable from one application to another, from a bash shell, run
heroku config:set MY_VAR="$(heroku config:get MY_VAR --app old-app-name)" --app new-app-name
To copy a Heroku ENV variable from one application to another, from a bash shell, run
heroku config:set MY_VAR="$(heroku config:get MY_VAR --app old-app-name)" --app new-app-name