Buttons are triggers only can only be activated from the device itself. In the new app you can assign actions to a button press or held action (if supported) or via custom apps which support buttons.
If you want to trigger an action manually try creating a virtual momentary switch (it resets itself after a push). A momentary is missing from the new app as of now but you can create your own virtual momentary switch by creating a device in the IDE using the Momentary button tile DTH.