During the return process, we are using the same process order as in the initial.
We have 2 steps:
1. return of the goods
2. creation of the Credit note document
Return of the goods
To return goods issued by the delivery note document, open the delivery note details and select the Return goods option.
A new delivery note window shall appear. Using the negative quantities return the returned items.
Creation of the Credit note document
After approval of the returned goods delivery note, select Create credit note option.
Within the currency window, select the desired currency. Confirm your input by selecting Create button. 
A new Credit note window appears. Enter the service item with a negative quantity and amount.
Save the changes using the Save (F9) button and approve the document.