What happens if i accidently forget to recite ziyarat e ashura one day or for a couple of days. does this mean i have to start all over again or just keep on reciting till i reach the 40 th day.

Actually the number 40 itself has its importance so we should complete this number without any gap as in any amal continue and presence of mind is a major factor it shows how much the one who’s doing that is devoted to it. So if possible you continue once you have started it till end.