How to make the ball reset to it's starting object?

I have completed the Roll a Ball Tutorial and would want to make some modifications. Is it possible to reset the sphere’s (player) position when it falls out of the plane (ground)?

Check the Y coordinate of your ball.
if it is lower than the plane’s, then reset the ball’s position.

@this-play I’m really new to C# language could you care to demonstrate the script/code?