By default, the On-Demand questionnaire cannot be re-recorded. However, if the employer has setup the position to allow you to re-record the questionnaire, there will be a "Retry" button at the Submit step.
If you click "Retry", your previous responses, including written responses, will be erased and you will start fresh at the beginning of the questionnaire. The recruiter will not be able to see your original questionnaire. You cannot re-record individual questions.