The pendulum is responsible for making the clock keep time. If your clock runs too fast, you can move the pendulum-disc down a little on the pendulum to correct this. If the clock is running to slow, you have to move the pendulum-disc up. This should also be described in your clock’s setup instructions.
Keep in mind that moving the pendulum leaf or disc 1/8 Inch (3 mm) on the pendulum stick is equal to a 3 minute change in a 24 hour period.