How to change PO Requisition Charge Account based on Requistion line DFF value

How to change the charge account in the PO Requisition distribution form based on PO Requisition lines DFF values.

Example:

Line DFF value:we have two values A and B in the list.

user will select either A or B.If user selects A then account(segment12) should generate with A.If User selects B then account(segment12) should generate with B.

IF attribute13 = A Then

charge account should be 123-765-000-A-000-000 (Combination of segment9,segment10,segment11,segment12,segment13,segment14)

IF attribute13 = B Then

charge account should be 123-765-000-B-000-000

we are using 11.5.10 version.Can you please advise me.