If you are asking how to change the compiled Godot icon then you can either override the Godot.ico file (for windows) and the logo.png files (for the other platforms), or you can edit the resource files and changed the linked icon. I would personally recommend just overriding the icons as it’s easier. (NOTE: I have not tried either method, I’m just doing some guessing based on limited knowledge of the Godot code base)
If you are asking how to changed the exported project/game icon then I’m afraid to say there is currently no way to do so. Hopefully we’ll have a solution in the future, but as of right now there is no way to changed the exported project/game icon.
