Sysapproval_approver related list for change_request

[ditu]

Hi, 

sysapproval_approver table -

Display value - "Approval For" referencing to Task table

Still, when I "Edit" the related list for sysapproval_approver on a change form, it gives me a collection of users to select from and add new record to related list. 

How is this functionality achieved?

[ditu]

FYI: I intend to achieve a similar functionality on another table. 

In change request, when I click edit on this related list, It lets me add new approvers (users) to the change. In my case, this value is coming as Reference Field (Task list).