There will be times when an applicant will apply to the same Job more than once. In this situation, it is important to remove one of them from your Hiring Process without alerting the candidate of Stage changes and causing confusion.
To begin, click the gear at the far-right end of your Job's Hiring Process bar.
Next, click into the settings for your On Hold Stage.
Once inside, select the dropdown in the "Automated Messages" box.
Select "None". This will stop automated emails from sending to candidates you add to the On Hold Stage.
Once you click "None", the "Automated Messages" box should be empty, like this:
Now that you've turned off its On Hold messages, go back to the Applied Stage in your Job's Hiring Process.
Click the three-dot button on the right side of the row of one of your applicants. This will be your "non-active" duplicate.
Click "Move to Stage".
Select "On Hold".
The non-active duplicate will now appear in On Hold. Now you can leave them there and progress the other, "active" duplicate moving forward.
Finally, return to your Job's Applied Stage, and progress or reject the active duplicate as you see fit.