Change material using buttons

HI all.

As i said in the title of this question, I’d like to change material of an object in runtime. Here what I’d like to do. In my scene there’s a a cube with a BP (image 1-3) and i’m trying to put the 2 buttons i created (image 2) in the scene when the player is near the cube. I managed to put the buttons on the scene but i don’t know how to put the action on them. Well, i know that there is the alt textoption “OnClicked” but I can’t link the action with my function (image 3). I want also to know how to put the image of the material i want to change on the button or, if it’s possible, how to do a box with all the possible changeble material of the object.

Thank you All