On the left hand menu select "Orders" then "Deliveries"

Select the delivery you would like to request credit for by clicking →

Find the products you would like to request credit for and select the tick box next to the product code

The request credit button will appear

Click "Request Credit"

Enter the Qty you would like to request credit for

Add any notes

Click "Request Credit"

An email will be sent to your supplier requesting credit for all products selected

Credit queries moved into Credit Notes Tab