Dominoes Extra Button

[Frandra]

My dominoes Extra button shows the water bucket in the Headless Horsemen quest "Stop the Fires!" I want to bind it (or move it) to a button so that I do not have to click it each time is use it. Can anyone help me figure out how to do this? I really am not a Noob but I just can't seem to wrap my head around this. Thank you.