If a Candidate has been made Inactive on a Shortlist. There are two different ways of making that Candidate Active on the Shortlist of the Vacancy.
The first way is by accessing the Candidate Contact record and clicking the As a Candidate tab, placing a tick next to the Inactive Shortlist you'd like to Reactivate, click the Ellipsis, Click Activate
Choose the Status from the drop down that you'd like the Candidate to be in.
Click Activate
The Shortlist has now been reactivated and is in the Status you selected. Manage the Candidate you would normally moving forward.
The second way of Reactivating a Shortlist would be from clicking the Shortlist left side menu. Change the View at the top to "Inactive shortlists", find who you are looking for using Quick Find or looking through the list, put a tick next to the name and click Activate
Choose the Status you want the Candidate to be in
Click Activate
You can then find the Candidate again easily by changing your view to "Active Short Listings" and you will see your Candidate at the top of the list as they are displayed in Modified On order.