Steps to add a button

I want to add a button next to the hangup button. Others have asked how to do this, but it would help if someone could walk through the steps to duplicate the hangup button, i.e. there would be two identical hangup buttons and clicking either of them would leave the meeting. Specifically, which files need to be changed?

See Toolbox.js (web and native)

return (
             ... you can duplicate another HangupButton here 

Since HangupButton is already listen to click event
_handleClick which is extended from AbstractHangupButton class.
click either button will hangup.