The Employee Reimbursements application is created in the Creating a New Pega 7 Application lesson. Then over the next couple of lessons, the case types are created and elaborated on.
Click on the HR Services app name in the header bar (to the right of the Pega 7 and Designer Studio icons), and hover over Switch Application. If you completed the previous exercises, you should see both the HR Services and Employee Reimbursements applications. Click on Employee Reimbursements to switch to that app.
If you do not see Employee Remibursements, then you must complete the previous exercises as noted.