Its also pretty easy to change the default logo using the web modeler
https://docs.mendix.com/web-modeler/theme-customizer-wm
Your current icon should exist within your theme folder.
All you need to do is replace it with the desired icon – it might be named something like favicon.ico
If you cannot find it, within the theme folder edit your index.html and it should contain a reference to your icon. You can replace it at that or add another image and switch the reference.
Hope this helps.