In the souce there is a folder somewhere with the src and builds and other folders, inside there there is a .ico ile that looks like the TPT logo. Then to change it make a 16x16 (and a 32x32 I think) png file repersenting your new icon and google png to ico and there is a website, upload yours (You can't just rename the png, won't work) 

and it will email you back your ico, then just change your icons to the name of the icons there.