You can change the app icon from "App Icon" in the Settings screen.
In rare cases, the new app icon is not applied correctly or reverts to the previous one.
This is an iOS issue and can be fixed by restarting your device.
Restart your device, and then try changing the app icon again.
The app also offers icons showing the year or month numbers.
These numbers do not update automatically — they need to be changed manually.
iOS currently does not allow apps to change their icon automatically. As soon as this becomes possible, we plan to add it.