Casting to widget

hi i’m pretty new to unreal engine and i have a hard time trying to understand the cast to function despite the many tutoriels. I’m trying to make a 2d game and when a widget is drop on another it change it change his own texture and the texture of an other droppable widget.

the way i try to do it is by call an event in the case receive by the uniform grid but i still need tto cast it some how and i really don’t how to make it work.

If anyone would be so kind to help me understand? thanks in advance