Unable to add record/data in the Additional Assignment Info page in the quick action

Summary:

We need to create a custom job role having the ability to only view and manage Additional Assignment Info of employees via the Quick action section. We have assigned the Manage Additional Assignment Info and View Additional Assignment Info duty roles to the said job role. However, we are not able to add an additional assignment info/record as the 'Add' button is not showing/missing. What other duty role or privilege do we need to add so that the custom role that we have created will be able to add an additional assignment info/record to a user.