The Cardiogram companion app for the Apple Watch requires WatchOS 6.2. and above. If you no longer see the app on your Apple Watch, please be sure to download the latest version of WatchOS. – How To Update your Apple Watch
The Apple watch face can be customized by selecting different complications. Apple’s instructions for adding a complication to your Apple Watch face can be found here. (Note that not all watch faces allow you to add complications).
As always, if you need any help, reach out to us by email at [email protected] so we can investigate this for you.