It bothers me when I see a rectangular flame icon near the macOS logos and Adobe products. I made two rounded versions for use(it can differ from macOS versions).
The application is simple. Right-click to Flame icon > Options > Show in finder, Right-click to Flame icon from the popup window > Get Info, Drag and drop desired .icns file over the small logo from the get info window.
Open Flame as always and the application logo will be changed right away.
Hope this helps those who are annoyed 