You cannot reverse GR in Inventory only.

You need to do the following steps :-

Step 1. - Materials Management (MM)

Create and process a return delivery with reference to the original purchase order using the functions of Inventory Management (IM).  Make sure Movement type is 102 and stock type indicator to the stock to which the goods were originally posted with the usage decision (for example, F for unrestricted use stock or S for blocked stock). 

Step 2. - Quality Management (QM)

Cancel the inspection lot in QM using the function to change the usage decision.

Logistics - Quality management - Quality inspection - Inspection lot - Usage decision - Change with History - Usage decisions - Functions - Cancel lot 
 

How can we reverse the GRN ?
Status : Insp Lot generated, Result recorded, UD done, Stock posting done (QI stock to Unrestricted stock).

Kindly do the following :

Choose Logistics -> Materials Management -> Inventory Management -> Goods Movement -> Goods receipt -> For purchase order -> PO number known.

- The initial screen for creating a goods receipt for a purchase order appears.
- In the field for the movement type, enter 102 (goods receipt for a purchase order into warehouse - reversal). 
- In the field for the purchase order, enter the purchase order number for the original goods receipt. 
- You can copy the purchase order number from the inspection lot.
- Choose Enter to display the selection screen for the purchase order items. 
- Select the purchase order item for which you want to create the goods receipt and set the Stock type indicator to the stock to which the goods were originally posted with the usage decision (for example, F for unrestricted-use stock or S for blocked stock). 
- Save the goods receipt and exit the Materials Management component. 

Choose Logistics -> Quality management -> Quality inspection -> Inspection lot -> Usage decision -> Change with history.

- The initial screen for changing a usage decision appears.
- Enter the number of the inspection lot for which you previously made the usage decision and choose Usage decision (UD). 

To cancel the inspection lot, choose Usage decision -> Functions -> Cancel lot in the usage decision screen.

*-- Prashant Deepak

SAP QM Books
SAP Quality Management Certification, Interview Questions and Configuration Reference Books

SAP QM Tips
SAP QM Tips and Quality Management

Best regards,
SAP Basis, ABAP Programming and Other IMG Stuff
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