By default it is tied to your organisation. You need to publish the app to the app directory for it to be available for everyone. Are there only particular networks where you want it to work? This requires additional configuration on the Yammer side. A clunky workaround is to create app IDs in the other networks where you need to run your app and allow the user to select the appropriate one. It depends on what you are trying to do.
Note : Verbatim copy from the Yammer Developer Network, as answered to my question here, https://www.yammer.com/yammerdevelopersnetwork/#/Threads/show?threadId=292877375