I did a lot of moving platforms in my game, its pretty simple
1- give your platform Bullet Behavior, and make sure it goes the way you want
2- make a line for it to bounce off of OR have it bounce off of existing terrain
3- Give this type of behavior: On collision with Surface > Set Bullet bounce off Surface +Set platform Mirrored
You can check it out here
http;//neoknightalpha01,bitballoon,com/