Click on Create Release Like you release a new version, but instead of uploading an apk click "Add From Library", Here you will get all the previous versions of your app, select the version you want to rollback to, then release it after review button.
in play store classic version , developer console gives an option for Halt rollout . if you will Halt rollout than current version of your app , will be unpublished from play store. Now we can published new version of app.