How to Install Icons from a Theme

Step 1. Open Shortcuts app:

Step 2. Add new shortcut:

Step 3. Tap Add Action button:

Step 4. Select Scripting option

Step 5. Choose Open App

Step 6. Select the app you want to add:

Step 7. Click on More button

Step 8. Tap on Add to Home Screen:

Step 9. Type the app name and tap on app icon:

Step 10. Select the Choose Photo or Choose File option:

Step 11. Select desired app icon:

Step 12. Tap Add button:

Step 13. Hooray! Custom app icon should be at Home Screen: