Unfortunately, there is no Xfinity Starz app. But, you can still watch Starz through Xfinity using the Xfinity Stream website on a PC. You can also download the Xfinity Stream app from the Apple App Store, the Google Play Store, or the Amazon App Store for smartphones and tablets.
Can You Watch Starz App With Xfinity?
Can You Sign Into Starz With An Xfinity Account?