Need system to auto-populate descriptive flexfield values in Responsive Self Service Procurement

Summary:

Need system to auto-populate descriptive flexfield values in Responsive Self Service Procurement

Content (please ensure you mask any confidential information):

We have a requirement to auto-populate the values of descriptive flexfields on the Requisition Header level based on the following dynamic selections:-

1. If user selects Smart Form A, then the values of the DFF should default to "A".
2. If user selects DFF1 value as 'P', then the subsequent DFF2 should default to 'Q'.

Similarly, we want to dynamically update the DFF for other such combination of selections as well.
How can we achieve this through writing Business Rules in Responsive Self-service Procurement?