How to mandate some field for approver in each stage in CHANGE workflow

How to mandate some field for approver in each stage in CHANGE workflow

Hi,
I have a major change workflow in my org. In my workflow, every approver in own stage should be fill some field and approve stage for move to next stage. As matter of fact, I want to mandatory some fields to be fill-in before closing some stage of the Change Request. For example I want to mandate below fields in stages:

Stage1: Submisstion
      category

Stage 2:
      CAB Member

Stage 3:
      Risk, Service Affected, Asset Involves, Some custom additional field

Stage 4:
      other custom additional field

Stage 5:
      none

What should I do?

SDP v11.2.02
DB MS SQL

Thanks for helping