How to fetch value in new Student document from Student Applicant?

I added custom field “IIN” to document Student Applicant and also I added custom field “IIN” to document Student.
I need when to create new Student Applicant and fill in “IIN” after submiting document to add value of IIN to document Student.

How to do this?
I think I need use Fetch From? What command should I use?

For documents Student from Studen Applicant I used command:

doc.item_code.IIN

But now I need use similiar fetch on from Student Leave Application to Student Attendance for select type of value.
And the same way doesn’t work for me.
doc.item_code.absent
How to do it?

I’m surprised that doc.item_code.IIN is working for you. It should be just doc.IIN.

doen’t work doc.absent anyway.

actual!