Right approach to change materials of actors by widget

Yes this above is the LB.
And no, Left grip didn’t print a string while try to select the FALK-TR actor.
I have 8 FALK-TR actor BP in my level, numbered from FALK-TR1 to FALK-TR8

I don’t use as far as I know and can see the Left grip button of my controller elsewhere in BP’s in this project.