I decided to read ziyarat e ashura for 40 days so my wish can be fulfilled, right after 5 days the wish came true. I kept reading ziyarat e ashura to keep up the 40 days. However, yesterday i missed reading it, do you think i need to do 40 days all over again or can i give sadqa and finish it altogether?

If you did not say Wallah you will read it for 40 days you do not need to continue the reading as it is not Wajib. It was just a promise you made and it’s ok to break it as long as not bringing the name of God. It is recommended to complete the 40, even if you missed a day you can continue until you reach 40. Or you can read it twice in one day to catch up.