To add custom fields to the pre-employment form:

1. On the left panel of your admin dashboard, head to People > Settings.

2. Click on the Pre-Employment Form tab.

3. On the top right, click Update Form.

4. To add a custom field, click Add New Field

5. Select Custom Fields.

6. Confirm by clicking Save.

Read more: 

How to send the pre-employment form to new employees