You can't for now
As j4velin mentions in the FAQ in the app, it's not possible right now because only a Notification Priority 1 app can remove the icon. But other app like Notification Weather (in the Pro version) can remove the icon with a priority 5. So there is a way. I hope J4velin will find out how because that's the only annoying thing about this app. The rest is pure gold. I prefer this app to the built-in Notification toggle of Codename(Android) by miles.
How can I disable the icon on the status bar.
Even I choose "transparent" there's still a space for the icon.
As j4velin mentions in the FAQ in the app, it's not possible right now because only a Notification Priority 1 app can remove the icon. But other app like Notification Weather (in the Pro version) can remove the icon with a priority 5. So there is a way. I hope J4velin will find out how because that's the only annoying thing about this app. The rest is pure gold. I prefer this app to the built-in Notification toggle of Codename(Android) by miles.