While reviewing the applicants of a job, you can move candidates into the 'Reserved' list so that you can quickly go over the list if any of the assigned candidates can't make it.
Jobs >> All Jobs >> click on the eye icon against the job >> Assignments >> click on the Move to reserve list icon against the candidate you want to move to the reserved list.
To view the candidates in the reserved list, click on the Reserve icon.
The list of candidates will appear. If you want to assign them to the job, click on the hand icon against the worker.
You can also check the Jobs >> Applications list to have a quick glance at the jobs with Reserved list and click on the eye icon against the job to go into the Job Information window to action it further (as per the instructions above). This list makes it easier to look through the jobs where you have placed candidates on the reserved list.