Hello, I am trying to change textures of objects via buttons in VR space

I am using Oculus rift touch... I got buttons in canvas ... and am trying to change texture ingame of an object in VR space... via each choice i make from the dropdown menu... how can i do this? also i can't get the interaction of the buttons to work, even when i got OVRAvatar, FPS controler,... i canwalk, I see the touch controlers and my hands in VR space but still cant get raycaster to work and interact with the buttons. Can you help me?!