Send agreement to 2 participants and assign special fields to them - using rest api

Hi,

I have an pdf document created by my manager.  I have a application that has the user prefilling the fields. And in the document there are 2 fields the 2 persons need to sign. Person1 has the index 1 and person 2 the index 2.  So when the first person has signed then person 2 can sign. But I can't find out how to have the field for person 2 assigned to him, resaulting in person 1 having to sign that field to be able to finish the procedure. I am using the reast api v6.

best regards

Robert