If you want to manually issue a credit instead you can head to Clients > select a client profile > scroll down to the 'Credits' section > Issue > select a credit you wish to issue > Issue credit.

Before you 'Issue credit' you can set an expiry date for the credit if needed. To do this toggle on 'Set an expiry date' > from the drop down calendar select the date you want this credit to expire > Issue credit.

Once issued the credit will then be displayed on the client profile and if you added an expiry date the date will appear on the credit too.