Change Blueprint Material on collision with another Blueprint

Hello everyone, it’s my first time posting here and I wanna thank epic and all of you for making my dream come true, creating video games !

I’ve searched and read a lot about this question, but I must be too dumb to understand this Cast to thing.

My plot :

I wanna change the material of a blueprint static mesh in my level (or only a static mesh placed in my level ? what is the best option ?) after a collision between my player and another blueprint who plays the role of a button.

For now I can succefully change the material of an object inside the “button blueprint” after a collision, but I’m not able to change the material of another blueprint. Here is the definition of my “button blueprint” :

What is the best option to achieve what I am trying to do ? I can’t figure out the “Cast to” node, do I have to do this using the Level Blueprint ?

Any help here would be gladly appreciated (sorry for my bad english)

Sorry if this case have been solved before.

Thanks in advance !

Cheers