How to Refresh assignment 3

I am trying to answer Programming assignment week 3, I changed some parts of the code (Exercise 3), and there is an error. I want to return the cell to the original format (before I added some parts), but it is impossible. I would appreciate it if somebody lets me know how could I refresh assignment 3? I used the reverse arrow or circular arrow below the Kernel button, but the content did not change.

Hello @Fatemeh_Yavartanoo

Welcome to the community.

Please take a look at this article which talks about it.

It helped. Thank you very much for this help. :pray: