So the simplest way to do this is to put the OpenDoor() function on your door BP.
In your button BP, you need to have a variable that’s a reference to the door BP type.
Make sure that variable is marked as “Instance editable”.
When you call your button function, check to make sure your variable is valid, then call the OpenDoor() function from that.
Inside of the viewport, select your button. You’ll see a space for the variable that’ll take a reference to the door. Use the eyedropper tool to directly select a door BP.
Theres a good tutorial here called “Your First Game in UE5” from Andreas Suika which contains (among many other things) a door that is triggered by a pressure plate: