The procedure used to erase the Asteroids high score table is the same procedure used on the Asteroids deluxe game.
Put the game into selftest mode. Refer to your manual on where to locate theswitch. For uprights it is usually inside the coin door.
In selftest mode you should see a display that looks similar to this screen shot below.
Asteroids high score selftest display
While in selftest mode, press and hold (all at once) "ERASED". This is the indication that the high scores have been cleared. You can now release the buttons and exit selftest., , , and . For each button pressed in selftest mode you should hear a tone. This is the normal (standard) behavior of Asteroids selftest. Once all 4 buttons have been pressed, you should immediately see a message displayed on the screen with the text
Asteroids selftest showing scores erased