To reverse GR after UD, you have to reverse UD which is not standard functionality provided by SAP - refer to note 175842.
Alternatives is to create a return PO item to send the received stock back to supplier. Once you post GR for the return PO item (movement type 161), the system will create a negative quant in 916 storage type. Depending on the customizing, a TR might be created to pick the stock from normal storage type to 916. Otherwise, manually create a TO to pick the stock to be returned. Once TO is confirmed, the negative quant will be balanced to zero which completes the process.