If you need to refund a customer, you can initiate a full refund from their customer profile. Uscreen does not allow for partial refunds, but partial refunds can be managed through Stripe. If you're using PayPal you'll need to initiate the refund within 30 days.
Navigate to the customer you want to refund an invoice for under People > People and click Edit. Under the Invoices tab you can click the Invoice Number and then click Refund.