[Closed] How do you add a custom bmp to a macroscript in toolbar?

I cant for the life of me figure this out.
I have a toolbar with Macro1, Macro2 etc in it. I want to replace Macro1 with a custom bitmap. I know you can choose from a predefined set of bitmaps by Rightclick – Edit button Appearance, but I’m looking to add my own bitmap.
Is this possible? If so does anyone here know how ?
Thanks