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