You just have to edit the addon image files using any image file editor which supports transparency, for example GIMP or Paint.NET.
I don't see any reason to leave a 1 star review just for this basic question.
I hope you will consider changing it as it's discouraging to get such a bad review even if I provided lot of example configurations for the community, exactly to avoid people to waste time trying to create addons without examples.
Have a nice week.
