The deduction of credits from credit passes works completely automatically, but sometimes credits have to be added or deducted as a gesture of goodwill. You can learn exactly how this works in this article.
Search for the corresponding customer in the search bar and click on their credit pass. On the right-hand side you will find the buttons "+1 Credit" and "-1 Credit" with which you add or subtract one credit accordingly.
Click on the customer's product and select "Product details".
On this screen, click on Product details > Show. Below you can manually set the total number of credits available on the pass.
Attention: Changes to the credits initially only affect the available credits and do not automatically change the price. If you add a credit, you still have the possibility to charge additional fees for this credit.