Unity Random Movement Script

I'am kind of stuck at a project. It is a little game. I'am trying to move a block in a rectangle map and it should bounce of the wall in a random direction but stay in the rectangle

I added a little force to it with the ridigbody

player.rigidbody.AddForce(30,0,0);

But I have no idea how to manage the random bounce of movement I appreciate every idea thank you!