Deployment to different cloud

first you should be system administrator on both environment. Go to devops section -> Deployment-> Add new environment-> provide the environment URL -> Then send request. 

Once the request is sent then login to other environment and accept it. Now you can select whether.

Now go back to your previous environment admin console and see you will start to get the list of environments connected. Select your other environment from list and enable external deployment check box. 

docs.appian.com/.../Deploy_to_Target_Environments.html