How to change the Siri icon on macOS Catalina?
Try this method
Open finder
Make a duplicate of Siri app
In duplicate find Siri.icns delete this
Prepare .icns file with your custom icon (you can find this in google already in .icns format or convert another format to .icns using converter
Drop it at the same folder where you remove Siri icon
Rename it as „Siri“ if it isn’t already named „Siri“
!! Important step! Delete your duplicate Siri app name and set another don’t use „Siri“ name
In order remove Siri from dock and drag and drop your new Siri to dock