Instructions
- Open the Shortcuts app on your iPhone.
- Under the My Shortcuts tab, tap the + button.
- Tap Add Action.
- Choose the Scripting option.
- Under Apps, tap the Open App option.
- Tap Choose, then select an app to customize.
- Tap the … button.
- Give your Shortcut a name.
- Select Add to Home Screen.
- Give your app a new name if you wish, then tap its icon and select Choose Photo.
- Select a custom icon image from your photo library.
- Finally, tap the Add button to place the icon on your Home screen.
For more details, visit https://www.macrumors.com/how-to/change-app-icons/