There is no built in way to roll back to the prior version of an application in WebSphere. For example, there is no roll back option in the WebSphere admin console, nor is there a wsadmin command that can be used to roll back. Instead, before you deploy a new version of the app, you would export the current version of the app.
Then, the exported EAR, WAR, JAR, or SAR can be used to return to the prior version of the app.