Hi,
There are a few ways to do this.
if you need to disable/enable the button regular, then you might want to place that object into a globals for easier access.
Then on trigger you can use Set Fsm Actions (for example Set Fsm Bool) or a 'Send Event (By Name)' and target the global.
if not many times you could also use 'find game object' at the start of the scene, to get a reference to that object