as a verb, 'undo' can be used to express the action of reversing or canceling a process. This meaning for the word has a slightly stronger connotation than the noun form, since it implies agency on the part of the subject.
1. She undid the damage done by the fraud.
2. Undo the last command to prevent a crash.
3. I will have to undo this terrible decision.
the word can imply the restoration of a situation as well as the removal or cancellation of something. Pay attention to the context when you correctly use the word.