macOS adds the prohibited image to the icon of apps that no longer run in the OS. fF you try opening the app it will likely give an error message.
There is a way to change the icon of apps (via the Get Info* window but that won't help you in this case.
* 1. Locate another app that has a suitable icon, open the Get Info window for the file in Finder, click on the icon image, command-C to copy it
2. Open the Get Info window for the destination app file in Finder, click on the icon image, command-v to paste the replacement icon ...