Be patient. The reset sequence (when you start a game) does three basic things.
Its resets the latching relay bank (look for a BIG arse solenoid that resets
several relays at once), and resets (in most cases) some steppers including 'ball in play'
and finally resets all of the score reels to zero.
Identify these things in your game and on the schematic. Lots of great
links others have already mentioned.
Steve