I have mentioned 2 scenario which is your scenario?
Scenario :1
If you are trying to return back to vendor with 100rps then below is solution,
Goods return is no enough bcz vendor have to debit so you have to follow the below step
Step: 1 Post goods return
Dr Cr
Goods Received Not Invoiced (GRNI) Clearing 75
Stock Account 75
Step:2 Copy to A/P Credit Memo
Vendor 100
Goods Received Not Invoiced (GRNI) Clearing 75
Materials - Purchase Price Gains/Loss 25
Scenario :2
If you are trying to reduce the stock
Step: 1 Post Goods Issue
Dr Cr
Material different gain or loss 75
Stock Account 75
Step:2 Do revaluation to get the correct item cost
Dr Cr
Stock Account 25
Material different gain or loss 25