In some situations, you may want to move a candidate backward a stage or two. If that is the case all you have to do is click on the candidate's name or search for them in the global search to open their candidate card.
From there click on the action menu, next to "advance", and select "Move Backward"
Clicking "Move Backward" will open the following modal where you will be asked which stage you want to move the candidate backward to.
Simply make a selection and click "submit" and the candidate will be moved to the stage you selected and their submitting recruiter will be notified of the update.