A button press is a ugui action, if you don't have them in your action list you need to download ecosystem and download it from there. Then it's ugui button on click action. So you setup on that button object this fsm, and this action will listen for clicks, on it's clicked just make it do whatever you need, play anim, hide or show weapon etc. You can setup as many states with this as you like, and then as many transitions to states too. So you can have 3 states, and all of them will have the button on click action.