I've had several students in my Captivate classes ask if it was possible to allow learners to retake a quiz. It's not only possible, but the solution is very simple.
Choose Quiz > Quiz Preferences. From the list of Categories at the left of the Preferences dialog box, select Settings. From the Settings area, select Show Score at the End of the Quiz. (This will add a Quiz Results slide to the project, which is where the Retake Quiz button will appear once enabled.)
With the Preferences dialog box still open, select the Pass or Fail category. From the If Failing Grade area, select Show Retake Button and then click the OK button to close the Preferences dialog box.
The Quiz Results slide will now include a Retake Quiz button. You can size and position the button anywhere on the slide just like any other button.
When the learner takes the quiz and fails, clicking the Retake Quiz button will automatically reset the quiz score. In addition, the learner will be taken back to the beginning of the quiz.
If you would like to see a demonstration of adding a Retake Quiz button to a project, check out the video I posted to the IconLogic YouTube channel.