Do you mean that at say 7am it boings 7 times and at half past 7 it chimes 7 again? That needs a techie.
If, as I suspect, it only chimes 7 times at half past 7 and only the (single?) half hour boing at 7 then you need to turn the hands to a whole hour chime, count them, and turn the hands to just past that position. Then you need to turn the hands to the next half(or quarter?) hour and let it boing before you turn the hands to the next position. Keep going like that until you reach the correct time but make sure you let the mechanism finish chiming before you turn the hands to the next chime.
I suspect the clock has stopped at some stage and someone has turned the hands to the correct time but did not wait for the chimes to catch up.
I know that my grandparents (no pun intended) were very strict with us kids touching any of the clocks for fear that we'd touch the hands and the chime would go out of sync.