Gamepad UMG Slider control

Hi, I want to set up a system where I can change the Sun position using an on-screen slider, by pressing and holding the Left Trigger of a GamePad controller.

I have set up the Sun Positioner Plugin with BP and UMG slider but I cannot set up the Gamepad Controller to interact with the slider.

I have watched tutorials explaining using UMG with Gamepad, but can’t find any explaining how to map the Gamepad Controller Left Trigger to the Slider.

Does it have something do with Keyboard Focus? Any help would be great as I’m a complete noob when it comes to BP.