From the Dashboard

1. Find the charge to be refunded in the Payments overview page.
2. Click the ••• icon to the right of the charge and select Refund charge.
3. Enter the amount to be refunded. The default is a full refund. For a partial refund, enter a different amount to be refunded.
4. Select a reason for the refund. If you select Other, you must provide an explanatory note that is attached to the refund.
5. Click Refund.

Using the Stripe API

Create a create_refund call in the API.

1. In the API call, include the charge ID to refund.
2. To refund an amount different than the full charge amount, include the amount parameter and enter the amount to refund. If no amount is entered, the default action will be a refund of the full charge amount.
3. Run the API call.

If you need any further help with this, please refer to https://support.stripe.com/questions/refund-a-customer.