The past tense of the verb undergo is underwent. This form is used to describe an action that was completed in the past.
For example:
- She underwent surgery last year.
- They underwent a series of tests to determine the cause of the issue.
The past participle form of undergo is undergone, which is used in perfect tenses. For example:
- He has undergone many changes in his career.
- The project has undergone several revisions before final approval.