Issues with git version rollback and Push

Question

Let me describe:
I now have 3 version numbers commit id: a, b, c. I am currently on c and have pushed it to the remote library
I need to roll back to b. Then edit and submit (if the version number is b1), and then push to the remote library. What should be done?

Question 2:
I need to save both the modification of b1 and the modification of c, then edit and submit, and then push to the remote library. What should I do?

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I finally reset --hard, then merged to the master, and the editing of the c node was discarded. Thank you everyone for your enthusiastic help

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The reason why I encountered this problem is as follows when I think about it:
When I was at node b, one requirement had been completed. I continued to work on the next requirement at this node, but I received a notification that I needed to complete the next requirement. Put the first requirement online, and that's it
So I should create a new branch after completing the first requirement, and continue to work on the next requirement on the new branch
Do you think this is the case?

Answer 1

You just need to know about git revert.

$ git revert b(a commit id)

Answer 2

What is the submission id? Falling back to 2 (what does 2 mean), the description is very confusing.

Answer 3

I don’t quite understand. Since I want to save the modification of c, I can just change it directly based on the c node.