Each time you reset the clock, a small adjustment is made to the speed. If you set the clock forward, it is incremented to run faster. If you set it back, it is decremented to run slower. If you make daily adjustments to the clock, eventually it will keep accurate time.

The mechanism that makes this correction is fragile and sometimes doesn't work. You would need a watch repair specialist then.

Try daily adjustments and see if it improves it's accuracy.