There is a basic data table to populate the reasons for that field.  Many list of value fields on the various pages can be extended by updating a list which is a separate page view.  The basic data pages tend to be locked down to the normal user and only accessible by an Admin or IT person.

Have one of your Admins check with full access and then the basic data tables can be seen.  You’ll have to establish the permissions for the IT folks you want to be able update and maintain these tables.

Within the Authorization process setup, there will be a tab to setup the Reject Reasons.

Thanks.