This particular feature requires job tracking feature to be turned on, you can do so by following this link.
On Web:
Click on Menu > Settings > Organization.
Toggle on "Assign Employees To Jobs".
On Mobile:
Tap on Menu > Settings.
Tap on > Organization > Info.
Toggle on "Assign Employees To Jobs".
Keep In Mind: Once assign employees to jobs is enabled, an employee can only clock in and out of a job they have been assigned to. In addition, the jobs list for reconciling a job, scheduling a job shift or adding missing job shifts for an employee, will be filtered by the jobs assigned to them.