Customize the icon for iOS Web App

Hello all.

I have 2 instances of hass containers running on 2 machines. I put a web app for each of them on my Home Screen. I would like to differentiate them by the icon.

I have successfully changed the favicon.ico on one of the instance. But I have a hard time figuring out where the apple-touch-icon.png is.

Could someone give me a pointer? Many thanks.

P.S.
Why do I run 2 instances? One of the reason is redundancy. I discovered that HASS hangs sometimes. As I use HASS automation to change the Ring Alarm mode based on clock. It failed to disarm in the morning a couple times.