GameMaker - Asteroids Part C

The one thing that I didn't get was how he made the game restart when he pressed R at the game over screen. In the video he never shows how the code would work or pressing it at all, so I added the code myself as he never showed it. I added a instance event in the destroying event in the small asteroid code so every time a small asteroid gets shot, another big asteroid spawns making the game harder.

https://drive.google.com/open?id=1IUvkBtyGBEHHqzN5c0lna9vwuHWPbuJD